I'd have to say Panasonic 3DO FZ1 for best looking console of all time, really smart design (front loading based on VHS style) and looks unlike any other console before or after it. Most people probably never heard of it, was out between 1993 and 96, wasn't very successful due to it's stupid price at the time but built up a library of around 200 games over it's time with some pretty decent ones (though also a lot of interactive full motion video titles too). The system looks especially cool when both the (green and red) power and disc access lights are on.
I also like the simple clean look of the Sega Dreamcast and the Sega Multimega, a rare combination Megadrive and Mega CD unit all in a box a little smaller than a Nintendo Wii, really smart looking console and getting collectable now (wish I'd kept mine). As some other ppl have mentioned I also quite like the look of the original Megadrive though think they spoiled it with MD2.
As for the current gen, I think my favourite is the 360S, really good improvement on the original and looks a bit more appealing than PS3, though I wouldn't say I mind the way the PS3 or Wii look either, just not quite as distinctive.