I run Bell Dirtster 26x1.75, rated to 65 psi max, but I usually have 60 psi in them. They have kevlar flat protection and only cost $15/tire. Of course, I don't put a lot of weight on my bike (me + ~50lbs max tongue weight) because I pull a trailer.
On my R20 I've got about 800 miles on them with no problems. On my Kona (my primary trailer puller), I've got about 500 miles on them with no problems.