Hard to beat a pair of Performance Triflex tights:
http://www.performancebike.com/bikes...400066__400066
or
http://www.performancebike.com/bikes...400066__400066
over regular road shorts. They're insulated and windproof but not waterproof. I've done 75 miles in 36° and steady rain in a pair. I don't know how cold they'd go in the dry, but quite a bit colder. Of course it makes a difference how hard you ride, so someone else's temperature range may not be yours. You could also go with the chamois tights. I'd rather wear my regular road shorts with a good chamois and have double over my privates, but that's just me. For baselayer then I'd just wear leg warmers, nothing inside my chamois.