I hike in running shorts in the summer, hiking pants in cooler weather. I have a pair from Columbia. I put a drawstring in them so I don't have to wear a belt. Makes it much more comfortable when carrying a 25-30 pound pack.
I would say army surplus acu or bdu pants. I mean hell the 10 years I was in the army I did plenty of walking/marching/hiking or what ever ant they did the job just fine.