As you may already know, Android is technically
Linux, although it's quite different from other distributions (No GNU or X.org for example)
As mentioned above, there is also Plasma Active and the Spark tablet (or whatever it's called now)
And I remember reading that Canonical had plans for Ubuntu tablets:http://www.omgubuntu.co.uk/2012/01/ubun ... ndroid-ios
No idea when it will happen though.