Honorable mentions go to the original PS3, and any other system with a glossy black finish. It looks nice if you don't touch it, but it's going to get fingerprinted/scratched to hell before long.
This. My PSP is no longer black, it's
fingerprints - that's it's color now. The phat PS3 is still much better than the Slim, though. It just looks cheap. bland & boring. Of course, the colored variants actually look pretty good but that standard, black one? No sir.
Otherwise, there are a lot of really old consoles that look pretty bad to me, you know, the oldest ones...Atari...Odyssey and the such. I know I might need a flame shield for that one. But I will need an even bigger one for what I'm about to say right now; I think the Supergrafx is pretty bad looking. It looks oversized, overdesigned, unpractical and on top of that, very plastic-y - I'd like to have one because of what it can do but certainly not for it's look.
You may flame me now.

Edit: Oh yeah, I just remembered that Viewmaster Interactive Vision-thing from one of the sales threads. That wins, hands down.