Another vote for Tinker -- that shit's so broken, especially with the wealth of huge, deadly artifact creatures, and abilities like Master Transmuter or Venser, the Sojourner to bounce them for additional ETB effects. So, so early on.

By that same token, if I were to make another category for land, Tolarian Academy is awfully awesome. :)

Counterspell

Snapcaster Mage. One day someone WILL break it wide open.

I'm noticing no one's put a red card on the list...

Since my fav dude, Emrakul, the Aeons Torn is taken, my second favorite card of all time is Primeval Titan. Reminds me of Force of Nature on crack lol. I mean, he can fetch ANY lands and if you have Amulet of Vigor and a Lotus Cobra or two out, man, SERIOUS ramp!!! Third favorite is Wurmcoil Engine. Just an awesome card that can go in any deck. Yep.

@ Agbu, the staple Lightning Bolt. A must for every red deck...

Necropotence

Banned or restricted in every format it was in at one point due to flat-out dominance. No other card is a multi-format powerhouse quite like this one is, including casual formats like EDH.

Lightning Bolt

Well it looks like we are a little low on lands for this deck and one of the most powerful lands is one that was just recently spoiled in Avacyn Restored. Cavern of Souls is great! You want your Eldrazi, Preators, or Giants (Titans) to hit without fear of counter magic... just tap this card and all of your worries are gone!

Emrakul, the Aeons Torn. In every format it is or has been legal in, it warped the way the format worked and played out. As it stands, it wins Legacy tournaments on a regular basis. It IS the strongest card ever printed. There's simply no arguing over that fact.

But as for the BEST card ever printed, I'd go with Jace, the Mind Sculptor. He brought on the first Standard banning in over 5 years, was automatically banned from Modern without even a chance, and regularly (and single-handedly) wins Legacy tournaments. He was the most expensive Standard card ever printed and remains to be the most expensive card printed in the last 5 or 6 years. He Brainstorms for +2, erases threats for -1, Fateseal-locks your opponent into automatic defeat, annihilates the game-state with his ultimate, and does all of these things for the simply cost of 2UU.

Broken in every essence of the word. Also, the best card ever printed.

Anyone who played against either of these cards is going to know what I am talking about.

Psychatog and Skullclamp. Both of them just turned the standard format on its head when they were available to players. Incredibly strong.

Yawgmoth's Will because what is more powerful than casting any of the previously listed cards? Casting them again!

I'll have to say Emrakul, the Aeons Torn. I've never used him personally, but every time someone uses it against me I lose. I hate the card to death, but it is simply amazing.

zendikar block full frame lands.

Hmm... This is always hard to answer. I am going to go with Flash+Protean Hulk based on the answers already.

Is this "best" as in "most powerful" or "best" as in, utterly perfectly designed wicked awesome?

I'm going to assume the former and just say Skullclamp. Never before has such a cute, innocent-looking little uncommon piece of 1-mana equipment been so dirty that it rolls in mud and atomic waste for its appetizer. And it's so cute!

Demonic Tutor: 2 mana and you get any card in your deck without a drawback. Talk about a toolbox card.

Sol Ring: Yields an extra mana on turn 2 with no drawback.

Mind Twist: Best hand denial in the game and with some mana ramp this card can win the game alone.

Sol Ring gives you 2 extra on your second turn, letting you spam 4-drops before most opponent play a spell.

Mana Drain for me. Whether it's better than FoW is debatable, but the advantage it gives you is undeniable.

Balance is the cleanest and most surefire way to crush your enemies, see them driven before you, and hear the lamentations of their women.

1. Time Walk
2. Jace, the Mind Sculptor
3. Brainstorm

Here are what I think are the top 7,8 of all time.

1. Force of Will
2. Channel
3. Ancestral Recall
4. Tie between Tinker, and Show and Tell
5. Emrakul Aeons Torn
6. Demonic Tutor.
7. Sensei's Diving Top.

There some awesome standard cards, but none of the standard cards compare to the ones in my top 7.

Skullclamp, I love this card! Its just so good. I loved the Elfclamp decks back in Mirrodin and this was my favorite card. Its insanely powerful! You just draw crazy amounts of cards.

Also Jace M S would be # 9, he is slightly just barely overated as far as being considered the 1 of the best cards of all time.

He will come out turns 2.3., which may seem semi fast. But the reality is that he will either get milled, discarded, before he comes out, or he will be countered, or he will be destroyed, bounced, killed immediatly after he comes out.

Being the 39 or 10 card of all time as JMS is or should be, is nothing to snide at. JMS is extremely powerful, and is very useful and is in almost every blue deck that its legal for him to be in.

That said JMS cant hold the jock strap of FOW, channel, Ancestral recall.

Lightning Bolt