Eyebrows, debadging, E46 headunit faceplates, turn signals (although they are "electrical", they are really just for show so more visual than anything else) sidemarkers, exhaust tips, wheels, tinting... Look at Torque's mod list.
You know, al the stuff that Woobie does to his car...
I agree with torque, although there are fewer mods to do inside that are difficult to pull off well with class and without being ricey, they wont have a place if we just do exterior mods.