After immortalizing mafia dons, deranged soldiers, and sex-starved butter lovers, what's left for a soon-to-be-80-year-old screen legend? Why, commercial voice-overs, of course! Yep: Marlon Brando, the Greatest Actor of All Time, is looking to give consumers all sorts of offers they can't refuse. Although the marvelously mumbly two-time Oscar winner has no gigs lined up yet, a demo clip of him pretending to pitch charities and cars now can be heard on the Internet (cedvoices. com): ''Celebrate who you are, what you've achieved, how far you've come, with the timeless symbol of success: the...Range Rover.'' Sold!