Originally Posted by
elbows
Look for a pair of BDUs at an army surplus or thrift store. They're very comfortable on and off the bike, pretty tough, and they have drawstrings to cinch the ankles and keep them out of the chain. I think mine cost me about $15.
The only downside is they don't breathe terribly well, so they can be a bit sweaty on warmer days.
I commute in uniform almost every day (normal uniform is a flight suit, but I prefer to ride in BDUs) and will second the comments on BDUs. The winter weights are definitely warm, but if you can find the summer weight they're not that bad (look for little boxes in the fabric). Also, since the USAF is switching uniforms, there should be plenty of BDUs hitting the thrift stores over the next couple years.