This is my first year of cyclocommuting, and I am in a similar climate to Tallahassee. Over the past week I have had to do some experimentation with cold-weather gear. I too made the mistake of bundling up too much.
I have found that above 50F, all I need are leg warmers in addition to jersey and shorts - not really for feeling warm, but to ensure the tendons/ligaments in my knees stay warm so I don't injure them. If it is really windy, I will wear a windbreaker in addition, but that is it.
From 40-50, I throw on a thermal long-sleeve shirt underneath my jersey, and if it is in the low 40s, a pair of thermal long johns, again mainly to ensure my knees don't stiffen up.
Under 40, same as above, just with the windbreaker. We don't get much lower than 30 here.
Oh, and gloves. Gloves are a must in cool weather - that windchill from riding can lock up my fingers very quickly without them.