Since I did this last year (but on my old mattexe_k account), I gonna post up the roster for Smackdown vs. Raw 2008. :O
Hardcore Holly (DS Version Only)
Marcus Cor Von
The Great Khali
Eddie Guerrero (PSP Version Only)
Jim Neidhart (PSP Version Only)
Sgt. Slaughter (PSP Version Only)
I was gonna put the non-playables on the list, but I thought it wasn't necessary. Also, credit goes to IGN for the roster.
EDIT: Oops. Forgot to add one more person in the Current Superstars list. D:
Oh, and according to OPM (Official Playstation Magazine), there will be downloadable characters for the PS3 version (and possibly the Xbox 360 version as well).
ZOMGDOUBLEEDIT: Sabu has been moved to the Legends list, since IGN has officially stated this.