I forgot to mention, against the Petrof I play Nc3 trying to provoke Nc6 and in the Four Knights I play the Halloween Gambit.
What's Your Repertoire, and why do you play it?
I play scotch game (1. e4 e5 2. Nf3 Nc6 3. d4) because (as has been said above) the lines are easy to remember and has open lines.
I used to play italian game (1. e4 e5 2. Nf3 Nc6 3. Bc4) because the lines were also easy to remember and offered good chances but I stopped because I disliked the line 3... Bc5. It also helped me with my smith-morra gambit :)
Against sicillian, I play the smith-morra gambit (1.e4 c5 2.d4 cxd4 3. c3 dxc3 4. Nxc3) because you get a great lead in tempo, you have the diagonals free for bishops and your queenside knight out, while it looks like black only has a missing c pawn. If black doesn't cover his/her weaknesses quick, they get in trouble! I also like to transpose into an italian game with this if they play e5. This is, easily, my favorite opening and all of my friends hate it :D
Against french I play advanced variation because it's fairly simple.
As black, against e4 I play petroff/petrov defense (1. e4 e5 2. Nf3 Nf6) because it's an equal game and there's really nothing outright wrong with it.
Against d4 I play nimzo indian (1. d4 Nf6 2. c4 e6 3. Nc3 Bb5) because it's a very solid defense for black and you end up hammering on white's weak doubled pawn.

As black, I play mostly the black side of Anti-Sicilian BS.
Just now facing 1.e4 for the first time on this site.
1...c5 2.Bc4.

As white, I usually play the Bird and queen pawns opening. The Bird because many players don't use the sharp and dangerous From Gambit, and also because it's quite originial. I was bored with e4, so f4 was a good solution. With d4 I really like the Catalan because of the fianchetto's bishop pressure on the long diagonal which really tortures black position
As black, in response to e4 I usually play the sicilian Sveshnikov, because of it's dynamism, it offers good counterplay. In response to d4, the modern Benoni for the sharpness and the complications of the games
Colle as White. French or QGD as black. People hate to play me.