Definitely HP Touchpad, if any. Right now, I'm running tripleboot - webOS, Android 4.0, Archlinux ARM (still using webOS most of the time).
I wonder which other tablets can do this - I hope some, but I'm not very sure.

You may also consider waiting for Vivaldi -http://makeplaylive.com/

EDIT: I forgot to mention that tablets in general are not that useful. Sure, they are cool, but I cannot imagine any task they're special for (maybe except for reading PDF's and magazines). So, unless you have really good use for it, I'd think twice before buying one.