Hey, I have a Macbook white (2.1ghz 2gb DDR2 800mhz 160gb hdd).
I would like to upgrade to 4gb ram, buy a 2x2gb kit.
What brands should I avoid and what brands should I buy?

I'm from Brazil, so it's not that easy to buy from sites that have "apple certified" memories, such as newegg.

Is there a rule or compatibility list with brands and models where I should check?

Thank you in advance and sorry for my miserable english.