The key is buying layers that can be used more then once to match the weather.

To fit under the jacket, I like long sleeve cycling jersey's of different thickness or insulating abilities. Some are thin and nothing more then warm weather jersey's with long sleeve and others are thicker with fabric designed to tramp heat and insulate the body, these are called thermal jersey's. When the temps warm up, I'll often wear a long sleeve jersey with a wind vest or the jersey by itself, whatever it takes to match the temps when used alone or added as a base layer.

Here is one example.
http://www.nashbar.com/bikes/Product...46_-1___202490