I saw no major dif between 03 & 04.   Only thing was that the tail lights and headlights had some minor cosmetic changes.  Personnaly I like the 03 version better.   I'm hearing some rumors on the other hand on 2005's, that it may inherit some of the 5 series look.   I hope not because I'm not to certain if I like that spacy look.   
go for the 03.