For the most part I try to creatively design my own unique decks. Broadly speaking, I'd say the decks I design have slow start, often ramping or playing combo set pieces, and then have explosive middle-late game power. This tends to work well in the 3-4 player group game format I most often play in.

In order of how much I like them, I'm most proud of (all updated for Ravnica):

• Big Life - which exploits a feedback loop to exponentially double my life total and has swung for 1,000+ damage on occasion. Somewhat hilariously, people keep telling me to remove the Serra Avatar because I guess maybe they don't see the feedback loop?
• Spiteful Stuffy Doll - which uses Spiteful Shadows and Stuffy Doll to win via non-conventional non-combat damage. This tends to be hard for some decks to deal with.
• Gaea's Avatars - Green ultra-ramp deck, which goes into all kinds of weird stuff: Primal Surge, Angel of Serenity, Craterhoof Behemoth, Akroma's Memorial
• Cackling Armada - I'm experimenting with Cackling Counterpart in a Selenya token deck to copy Armada Wurm and Thragtusk themselves (and not their token-spawn), then populating them to create armies of massive tokens and free token-spawn.
• Krenko's Epic Experiment - is another one I'm working on, though I can't claim credit for the concept. It basically uses goblins to ramp (via Battle Hymn and Infernal Plunge) into Epic Experiment which in turn plays Burn at the Stake and Goblin Rally. There are a lot of folks working on different variants of this concept and I like mine because it has the least focus on actually attacking with goblins and the most focus on the combo... but it probably still needs tuning.
• Heartless Golgari - A nice Heartless Sommoning Golgari build which uses Corpsejack Menace extensively.
• Guild Feud Reanimator - This is a fun one. Ramp into Guild Feud and play massive creatures. Also uses Unburial Rites and Faithless Looting. I love decks where you can cheat-cast.
• Charmbreaker Devils, Guttersnipe - For those who like to burn shit and break things. Creature hate, red burn, Guttersnipe for added damage and Charmbreaker Devils for recycling.
• Ravnica's Tokens - I have also updated my Cathars' Crusade deck to Magic 2013 and Return to Ravnica.