I found this nice adidas cycling jacket that is pretty much a windbreaker as far as size/bulk goes. It's got three jersey pockets, wind-proof, vented all along the bottom of the arms and most of the back too. T-shirt under that with a base layer (usually long-underwear type shirt) and I'm golden. The only thing I don't like is when I have to wait for the sweat on my back (the back venting only works when I'm not wearing my bag) to dry after a ride, which is pretty much like having an air conditioner on my back the whole time. It's great though cuz it's not so huge or warm and I can pretty much always keep it on indoors if I want to.