I'm with Sage, I like something cool to look at - so I've been sneaky.
I've taken the 'no-art' character sheets and layered B&W pictures of iconic classes (as montage)all over the sheet. Some bold and in the background, others very faintly overlaid in grey. This gives more than one image for the players to reference, usually covering both sexes and available races for the class
The ranger playsheet for instance has these images from artists I really admire (taken from deviant art mostly - obviously for personal use!) over/underlaid on the blank sheet: