Just so you know, do you know what two formats were most played by top players and judges when not in the GP?
1. General Legend Highlander
100 card highlander decks, 99 of which are in the deck and 1 is your 'general' who must be a legend and starts the game set aside and you can cast at any time. Your deck has to be built from the colours of your general's casting cost. Usually 4+ players per game.
2. Type IV (aka "The Stack")
About 500 cards in a stack made up of the most ridiculous creatures and spells in Magic (usually expensive/broken), no land, everyone draws from the same stack but keeps seperate graveyards. Just start with 5 cards in hand and you can play 1 spell per turn. Awesome fun, although as Rich found Desertion on Gleemax makes you something of a target for other players... and at 3 in the morning you don't want to have to choose where everything targets anyway because you're too tired. Again, usually more than 4 players.