I purchased a Seagate 500GB 7200RPM drive for my Unibody Macbook. It uses less power and is considerably faster then the drive shipped with the unit. Additionally it is extremely quiet. I think it is the best bang for the buck at the moment.
I plan on purchasing an SSD at the end of the year. Prices should have decreased significantly and Snow Leopard will be out by then.
Is it as quiet as the stock 5400RPM drive? How about the temperature? Is there a noticeable difference?