This has long been one of my personal favourite decks. It relies on the infinite mana combo of Pentavus + Dross Scorpion + Gilded Lotus:
1. Tap Lotus for 3 mana.
2. Spend 1 and remove a counter from Pentavus to make a token.
3. Spend 1 and sac the token to put a counter back on Pentavus.
4. Scorpion triggers, letting you untap the Lotus.
5. You're back where you started, but with 1 mana of any colour in your mana pool.
I like the combo because it doesn't reuire a specific colour, but can make any colour, so it's incredibly flexible.
Creatures
3 Pentavus
4 Dross Scorpion
3 Steel Wall
4 Vedalken Engineer
2 Memnarch
Spells
3 Gilded Lotus
3 Crystal Shard
3 Skeleton Shard
3 Fabricate
3 Thirst for Knowledge
4 Counterspell
Lands
4 Seat of the Synod
4 Vault of Whispers
12 Island
4 Swamp
To make use of the infinite mana, I have Memnarch to steal all my opponent's stuff, and Crystal Shard to make infinite 1/1 fliers. Other than that, Counterspell and Steel Wall help for early defence (Crystal Shard helps here too), Vedalken Engineer speeds things up a bit, Fabricate and Thirst for Knowledge help find the combo pieces, and Skeleton Shard recurs lost Penavuses (Pentavi?) and Scorpions.