Yeah BDUs are great; you can find them at army surplus stores. Cargo pants are awesome too; I bought a great pair at REI, they are the REI brand ones and they were kind of expensive but they can take a ton of punishment and I consider those pants to be money well-spent. They are breathable, cool in summer/warm when it's cold out, tons of pockets, durable, and the legs zip off into shorts. They also air-dry in like 10 minutes which is awesome if you get caught in the rain.
I also have two pairs of the APK capris which are excellent too, what with all the pockets. Their full-length cargo pants are good too but sadly are too long for me.