Runner's World has a funny tool on their page just for that:
http://www.runnersworld.com/cda/what...-0-0-0,00.html

This being said, below 10C I start wearing long tights, although as light as possible (not lined). I'd save the lined ones to below 3 C weathers. On top, below 10C, I'll go with long sleeve and probably a windbreaker most days, unless it's not really windy, not rainy, and sunny.

A small wool beanie is great (or a warm running hat, not the cool summer-type), light gloves are absolutely necessary for me. Warmer socks are nice, too, but I don't remember how necessary from last winter's experience...