It has to be PC3-8500 DDR3 1066MHz. A bunch of brands make it. If your looking to max it out, here are some options: http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007609%20600000445%20600000401&IsNodeId=1&name=8GB%20%282%20x%204GB%29
. You can read through the user reviews and stuff. That being said, be careful. Users have been reporting issues with Macbook Pros after upgrading them to 8gb of RAM. Specifically, it seems that when you initially boot up and the intel integrated graphics are being used (as opposed to the Nvidia discrete), there is a lot of screen tearing for a few minutes until the computer warms up. I just started hearing about it recently, and i dont know how wide spread of a problem it really is. It is probably a fixable firmware problem though.