I beg to differA more direct replacement for the podgy tyres on an MTB would be one of Schwalbe's balloon range.
Big Ben, Big Apple, or Big Apple Plus for extra puncture protection.
More comfort from the bigger air chamber and a more road-orientated - shallower - tread than some of the other suggestions.
http://www.schwalbe.com/gb/tour.html
Do they not look a tad 'lost' in there with the fork gap?FWIW, my Fratello has wheels with 29er rims (Mavic XM419) and I'm using Schwalbe Durano's in a 25 size.