My wife got me some 'Lambda' cycling pants for christmas, you can find them on amazon by searching "Cycling Wind Pants Tights for Winter Cold".

The coldest I've ridden in them so far is about 25f, and by the end of my 9 mile commute my legs were sweating. If it's in the mid 40s, they are downright hot for me. They completely block wind, and don't seem to get in the way of pedaling, even though they're not at all tight.

I have not ridden in the rain with them, but they are supposedly waterproof.