Here's what I wear for running in 15-20 degree temps:
-wind pants
-long-sleeved zip-neck T
-fleece vest
-light hat or fleece headband
-fleece mittens with long cuffs (I have Raynaud's syndrome so have to pay attention to keeping my hands warm or it will not be a good run)
-sunglasses if needed
-usually just my regular running socks and shoes although may try some of my hiking socks this year for extra warmth

This seems to work well for my 30-45 minute runs--I start out feeling chilly and then feel "just right" once warmed up. In colder weather or if it's really windy I'd probably add a wind jacket over everything else and possibly tights or long-underwear bottoms under the wind pants.