REI "Mistral" pants.
I start wearing them when commute time temps are low 50'sF and colder. Pricey, but really do the job of:

PRO:
1. Keeps my legs warm
2. Somewhat water resistant to light rain. Dries quickly.
3. Wind resistant up to about 15 mph.
4. Stretchy fabric - great for the knees.
5. Black - so hides dirt.
6. Aren't "bikey" clothes.
7. VERY comfortable!!

CON:
1. Pricey. Right at US$100
2. Pockets could be a little deeper.
3. Only five belt loops. I prefer pants with seven, but they are hard to find. Usually seem to have at least six. REI cheaped out on belt loops.