Apple doesn't have their "own" RAM... from what I remember, they actually use Samsung (and possibly other brands) RAM as "their own." If you buy from a reputable third party, such as Crucial or OWC, you will be fine! Apple's is more expensive anyway. You won't get more beachballs from good third party RAM, don't worry...
In fact, to make it easier, Crucial even has a selector where you pick your Mac model, and the site shows you the correct RAM for your machine