To the original poster and the one above I have just got these...
http://www.wiggle.co...yre/5360042609/
They seem very good. The centre section makes it quiet and efficient on road, and the side knobles come into play with a reduction in pressure for light off roading.
They are a jack of all trades, they will never be as good as a proper road tyre on the road, and wont be able to handle really muddy conditions.
But if you want to keep the dual ablility of a mountain bike they are worth a look, and they dont look silly on the bike either!
My previous tyres were Continental Speed king knoblies in 2.3
EDIT: One thing I did notice is that they have a much more rounded profile, and that makes them easier to turn or lean over. Just be aware that it might take you a few rides to get used to, I know for my first few rides doing a shoulder check, or even taking a hand off the bars to signal resulted in a bit of a change of course that wouldnt have happend with the old tyres.