I highly recommend Crucial. I used to buy from cheapie places, but since switching to a Mac Pro and Macbook, I've used higher-end RAM. I've had problems with cheap RAM that passes RAM tests, but still fails intermittently.
Don't skimp on RAM quality!
Agreed, buy from a reliable memory brand. Still, you don't need a spend a lot for memory these days. Just yesterday I ordered 2 x 2GB module for my HP 8430 notebook at $95 per 2GB module. The same memory is spec'ed for current Apple MBPs. I don't know about MacBooks, but with most PC notebooks you can easilly install the new memory yourself in less than 5 minutes.
