Stax Pieces
Armageddon/Ravages of War - Captain Sisay can fetch many lands, and we run plenty of non-land mana sources, so it makes these cards an automatic include. Trust me on this, if you can combo out or cast one of these, and combo out the next turn, cast one of these. If it gets countered, so would the combo, if it doesn't, they will spend their resources rebuilding somewhat, and you definitely won't get the combo countered the next turn.
Aura of Silence - This doubles as a tax effect (a meta dependent one, but very powerful), or as an overpriced Seal of Cleansing. It can be used as a sorcery speed Disenchant, but think of it more of as a threat, if multiple of your opponents want to cast an artifact or enchantment, not only is it harder to cast, but they also have the take into account that it might just be destroyed, and it might just slow them down a lot. That alone may in turn set you up to win the game.
Aven Mindcensor - A very powerful "three-sided" effect that can greatly hurt our opponent's cracking fetchlands, and obviously tutors.
Containment Priest - Shuts down reanimator, flicker effects, Flash-hulk combo, etc.
Dust Bowl - Great land, hits the lands your opponents need, if they are sitting on only one source of a color, blow it up, etc.
Gaddock Teeg - Shuts down Blue Sun's Zenith wins, Force of Will, Ad Nauseam, and a hundred other valuable cards, it does hit Paradox Engine, but fetching The Tabernacle at Pendrell Vale should do the trick to remove it on the turn you want to combo out.
Glowrider/Sphere of Resistance/Thalia, Guardian of Thraben/Thorn of Amethyst/Vryn Wingmare - Slows traditional storm builds tremendously, taxes tons of other cards, and most "free cast" cards like Force of Will take a huge hit.
Hokori, Dust Drinker - Fetchable Winter Orb on legs, valuable card in our arsenal.
Hushwing Gryff - Hits Kiki-Jiki, Mirror Breaker/Pestermite combo, Ancestral Statue/Animar, Soul of Elements, General Tazri, Breya, Etherium Shaper, Sidisi, Undead Vizier, Selvala, Heart of the Wilds's draw trigger, Jeleva, Nephalia's Scourge, Derevi, Empyrial Tactician, Mairsil, the Pretender, Reaper King, Sharuum the Hegemon, Riftsweeper, all of the allies, Phyrexian Delver, Trinket Mage/Trophy Mage, Recruiter of the Guard/Imperial Recruiter/Spellseeker, Snapcaster Mage, and so many more cards that I constantly face.
Kataki, War's Wage - Yes we run a number of artifacts, and yes this hurts them, but we only drop it against decks like Arcum Dagsson, or Breya, Etherium Shaper, and the like, or the guy with the insane opener of artifacts everywhere.
Linvala, Keeper of Silence - Shuts down dorks, other Captain Sisays, Thrasios, Triton Hero, Arcum Dagsson, Scion of the Ur-Dragon, Prossh, Skyraider of Kher's sacrifice, Breya, Etherium Sculptor, etc.
Sanctum Prelate - A bit of a strange card, but very versatile, can shut off Teferi, Temporal Archmage, hitting 0 can stop a Yidris, Maelstrom Wielder from storming off, and 1 hits a lot of cantrips, also, if you know the wincons of your opponents decks, it can shut them off too, remember to keep in mind you can always fetch The Tabernacle at Pendrell Vale if you need to remove it to cast a Paradox Engine or something.
Spirit of the Labyrinth - This card shuts down so many comboes, Azami, Lady of Scrolls hates it, Thrasios, Triton Hero sucks with it, and Tymna the Weaver isn't any better. Brainstorm is awful with it, and so is pretty much any other cantrip.
Static Orb - Ooh this is good, yes, it slows us down quite a bit, but it slows other decks down a lot too., It feels like a more global Winter Orb.
The Tabernacle at Pendrell Vale - Shuts off more creature heavy decks and dorks pretty easily, noted it can be used as a sacrifice outlet.
Trinisphere - Hits free spells like a bag of rocks, and most spells in cEDH get hit by at least 1 mana, if not 2 or three. Sacrifice to Kataki, War's Wage before combo-ing out unless you have 2+ nonland mana sources additional.
Tangle Wire - Gets progressively less powerful over time, but is incredibly good nonetheless. I like it much more than Smokestack.
Winter Orb - This is pretty much the best Stax card in the game. It terms of being colorless and having an incredibly cheap mana cost, it is very good.
World Queller - Naming land is always good, I mean with a Crucible of Worlds it is insane, but it hits a lot of other things too, always keep it in mind as mass edict.
Ramp Package
Arbor Elf/Avacyn's Pilgrim/Birds of Paradise/Boreal Druid/Elvish Mystic/Fyndhorn Elves/Llanowar Elves - These are the dorks, they get us mana fast and efficiently, and they do it all for one mana. Dropping a land and one of these is one of our best and most common openers.
Green Sun's Zenith - Count this as another dork most of the time. By casting it x=0, you can fetch Dryad Arbor, so in turn it is a 1 mana land-creature, or a mana dork.
Chrome Mox/Mox Diamond - These are the moxen, that for the effect of very fast mana, cost some cards in your hand. This is almost always is great opening hand to the point of causing insanely fast wins, but they can be decent even udner stax, if you need a couple more non-land sources to go off.
Mana Crypt/Mana Vault/Sol Ring/Grim Monolith - These are our colorless fast-mana. They give us ritual-like mana the turn we play them, and are even better the next turn. Insane in opening hand, and good otherwise.
Carpet of Flowers - A very powerful piece of ramp, especially because of the number of Underground Seas and Volcanic Islands it counts for too. Read the full text, because it can be activated only once per turn, but on either main phase so you can use it the turn you drop it if you move to the second main phase.
Candelabra of Tawnos - This can turn colorless mana into colored mana, unused Mana Vault/Grim Monolith mana back into lands that might not untap anyway (Winter Orb/Static Orb), and it can ramp us very easily with an Ancient Tomb or Gaea's Cradle and a couple creatures on the field.
Crucible of Worlds/Ramunap Excavator - Insane synergy with fetchlands, Dust Bowl, Wasteland, Strip Mine, World Queller, Armageddon/Ravages of War and is good in the mirror against other stax decks.
Mox Amber/Mox Opal/Seton, Krosan Protector - These are the fetchable pieces of ramp we used to combo out. You can use them earlier, but if they get wiped or anything, remember so you know you need more non-land sources before combo-ing out.
Combo Protection
Autumn's Veil - This is nearly a Silence, except it doesn't stop everything, and has the major upside of being able to be cast in response to removal or a counterspell.
Dosan the Falling Leaf - Great card in this deck, it is a worse Grand Abolisher, yes, but since it is legendary, we can use it as a fetchable one. This card is the main reason we don't run more effects like it.
Grand Abolisher - He is basically a one-sided Dosan the Falling Leaf that affects multiple permanents abilities too.
Silence - If we cast this before we combo out, yes it can be countered, but normally that counterspell that is now used up woudl be the only one countering the combo, and so there is nothing to fear. Very powerful, note it doesn't counter spells your opponents have already played, and while it is on the stack your opponents can still respond.
Mother of Runes - This protects Captain Sisay or any other creature like no other. Considered Devoted Caretaker for protecting Paradox Engine or Bow of Nylea or something, but can't find a spot.
Card Advantage (Tutors/Draw)
Captain Sisay - Yes, our commander is the best draw we have access to, and we always have access to it, and with something like 20+ legendary cards in our deck, we have a wide array of answers to find.
Eladamri's Call - This creature tutor at instant speed and to hand is greatly powerful, and was reprinted recently, so is a lot cheaper. This card is usually used to find something like a Hushwing Gryff or something so you shut off your opponents plan. We run 15+ really good silver bullets this can find. A whole sideboard worth of answers.
Green Sun's Zenith - This card can be used as ramp by fetching a Dryad Arbor, but can easily find a Gaddock Teeg or whatever you need to shut off your opponents' gameplan.
Sensei's Divining Top - This is a very powerful card, and though there are combos with it and good synergy (Counterbalance/Future Sight/Magus of the Future), we run it for the card advantage, it isn't an incredibly powerful card in terms of the normal understanding of "card advantage", but we run enough fetchlands and so much shuffling that it can be even better than a Ponder or Brainstorm would be.
Worldly Tutor - Its an instant speed tutor any creature to top. Useful to do on teh endstep before your turn, or upkeep of it. It is good to do it right before drawing a card so they have little time to think about it.
Yisan, the Wanderer Bard - This is a very powerful piece of card advantage, step one fetching a Mother of Runes, next time a Spirit of the Labyrinth, or a Thalia, Guardian of Thraben, then fetch an Aven Mindcensor or Vryn Wingmare or Sanctum Prelate or something, etc. For the grindy game against another stax deck, he wins games so well. Also tutorable by Captain Sisay.
Removal
Swords to Plowshares/Path to Exile - These are the white OG's, I mean they are one mana to remove whatever creature you don't want to exist. I mean occasionally you target your own Sanctum Prelate or Gaddock Teeg or Containment Priest if you realize they hurt you the most.
Nature's Claim - Staple in green for good reason. It hits so many high-priority permanents.
Unexpectedly Absent - Two white is the normal cost we use for this. It puts any non-land permanent on the top of it's owner's library. Do it in reponse to cracking a fetchland and they will cry.
Grasp of Fate - 3 mana for 1-3 high-priority non-land permanents is a great deal. Remember it is a may for each player, so use it as a Banishing Light or two if you don't want to mess with the guy with removal.
Mangara of Corondor - No, we don't run a combo with it, but it is our catch all removal spell on demand with Captain Sisay. Its like a Vindicate on steroids that our commander can fetch us.
Recursion
Eternal Witness - This is commonly used to recur a dead combo-piece, and is tutorable by all of our creature tutors, and very slowly by our commander by fetching Yisan, the Wanderer Bard and upticking him 3 turns, it can also be used to recur some stax.
Bow of Nylea - This is a combo card, but also is a tutorable piece of recursion to the bottom. This is almost always used mid-combo to return more combo pieces unless you can just straight up combo out.
Noxious Revival - This is a free spell for Paradox Engine, but is great at getting back a card we need. free and an instant makes it a good card.