Leatherneck,
I prefer the 100% cotton, ripstop USGI BDU pants for most of the year. They are light, dry quickly, roomy, have large cargo pockets on the side, pretty cheap, and available in multiple camo patterns as well as solid earth tones. The only downside I have found is that they are prone to tear right above the double-knee at the seam. This is an easy fix though with a sewing machine and lots of thread to reenforce the area.
For really cold weather, I prefer wool. I have been wearing West German surplus britches for several winters. They are constructed similar to the US BDU with cargos and reenforcement on the knees. They're super warm, wear well, and are a nice gray-green color that blends in well with most environments. I have recently purchased a pair of Columbia brand Gallatin Range wool bibs. These too sport cargo pockets, muted camo pattern, reenforced knees, and are toasty warm! God Bless! Jerry