I wear the same thing I'd wear for 60+ mile rides: whatever I happen to be wearing that day. Lately, that's mostly been these: New Italian Military Surplus Wool / Cotton Knickers - 636947, Pants at Sportsman's Guide Unfortunately, they've been sold out of my size for a while, and I'd really hoped to get more after getting a few pairs to start.

I work as a bike mechanic at a shop, though, so it's not like I'm in an office type environment....but these are great on the bike. Combined with some over-the-calf socks (sometimes with a second layer underneath), these have gotten me through this winter, and they're also reasonably comfortable on warmer days with the socks rolled down and cuff cinches open