of 2003- my top choice would definately be.......................
viewtiful joe- by far the most innovative game to come out and most interesting- it is tons of fun and worth buying a gc for
other notable releases for gc 2003 are: zelda: wind waker, fzero gx, soul calibur 2, mario golf, mario kart double dash!!, the gameboy player
thats all i can think of right now
but if you count japanese releases too then you must add tales of symphonia and baten kaidos to the mix- 2 great rpgs that i cant wait to see