I've always had luck with Kingston, personally. Some brands don't always play nice with some Laptops (or MoBos in Desktops). It's not a huge problem, but there are discrepancies out there with certain pairings.
Best bet is to go to an independent memory website (not Compaq, obviously, since they will have their stuff marked up quite a bit) and use a memory finder tool to get a list of brands guaranteed to work in your system. After that, hop over to Newegg and see what's the cheapest. Don't forget to read the reviews to see what others think of it as far as quality.