smurf I LOVE THEM. Not a major fan of their newest CD, though. Their first is my favorite.

I actually can't think of any bands off hand that sound exactly like them, but they've always reminded me of Akira Yamaoka's work for Silent Hill (why, I don't know).

For some reason my mind is telling you to check out Cocorosie, Sia, Garbage, and Blonde Redhead. None of these bands sound like Portishead in particular, but they all sort of remind me of one another for some reason or another. Check out Chad VanGaalen, too.

edit: Zero 7 comes to mind, too.