You don't need to go all the way to 25mm. For mountain bike purposes, I'd call anything 37mm and narrower to be 'narrow." Here's a few more possibilities.

http://www.wiggle.co.uk/continental-...rix-road-tyre/ comes in 25mm
http://www.wiggle.co.uk/continental-...city-mtb-tyre/ comes in 28mm
http://www.wiggle.co.uk/schwalbe-mar...acer-mtb-tyre/ comes in 32mm
http://www.wiggle.co.uk/schwalbe-koj...igid-mtb-tyre/ comes in 37mm
Plus, if you can find them, Primo Racers come in 25 or 32mm widths.