What is a good buffer to buy?

Hands down the Porter-Cable 7424. If you Google search it, you'll find numerous places with it. In the detailing thread, I have a link to a good deal on one that comes with the different pads and what not. Whats nice about the 7424 is that it rotates off-center, so that it does not always keep going over the same spot, which makes it harder to burn through your paint. The cheap buffers you buy from Sears, Wal-Mart, etc, all have a fixed-axis rotation with a speed of "on" and a speed of "off", which makes it nearly impossible to properly apply the different products correctly. The 7424 has a dial of 1-6 with 3 speeds between each number, so it's basically infinitely adjustable speed wise, which is what you really want!