I have the worst luck keeping these people's names/identities straight. Here's a little tutorial for myself and anyone else who has the same problem.
Keith David / David Keith
There's probably a more delicate way to put this but, simply, Keith David is the Black guy and David Keith is the White guy. Saying "Keith David" is usually the sure bet because he's been in a whole hell of a lot more films than David Keith -- at least I see more of Keith David's appearances (THE THING, THEY LIVE, ROAD HOUSE, etc).
Warren Ellis / Harlan Ellison
Warren Ellis is a renown comic book author (recently branching out into fiction with Crooked Little Vein) while Harlan Ellison is a science fiction author from way back ("Star Trek," A BOY AND HIS DOG, etc.).
Rip Torn / Rip Taylor
This one really took me a long time to keep straight. It just doesn't make sense to me that Rip Torn as a 'joke name' where he can be a pretty serious actor while confetti-throwing funny man Rip Taylor has the 'normal name'.