Zone of the Enders: I Dolores is pretty catchy.
The Second Runner's even more so, but that's a game.
Melphina's song from Outlaw Star.
Pretty much every theme from Cowboy Bebop.
Eva's opening theme (Say what you will, that's a catchy theme.)
RahXephon's opening theme (Never watched the show, but the theme is a standout.)
Noir's themes made that show.