I commute in those conditions for most of the year. I wear REI OXT pants. The legging on the pants is narrow enough that I don't have to worry about it getting caught in the chain. The pants are very breathable, stretch well, and they are not "spandex like" at all - i.e. they are not form fitting. The closest thing that I can compare them to is a track and field pant. I really appreciate the breath-ability since I have wear a waterproof pant over the top of them frequently when the rain starts coming down hard. If it's just a drizzle I just ride in the REI OXT pants because they are very quick drying.

http://www.rei.com/product/778310

I do wear a spandex/lycra/cotton underpant underneath the OXT's to keep things in place so that they don't move around so much on the saddle.