Sometimes no-name RAM can be just as good as the best brand name stuff, but then there are also times when you get some stuff that just flat out doesn't work. I tend to stick to brand names myself.

As to where to look... NewEgg is one of my favorite online retailers for computer equipment bar none. They're not always the cheapest, but they're always competitively priced, you always get what you ordered, and in a timely fashion. I don't know what more you can ask for. You can check any site you want that reviews online retailers, they'll all give NewEgg one of their highest ratings.