You can often get Crucial RAM cheaper than their site, though. Find the type you need from there, then look around elsewhere. Frys often has good deals with rebates, I got mine for around $21.
NewEgg.com is the popular place to buy components like memory and hard drives. A four GB upgrade is pretty inexpensive and definitely will make your BlackBook faster. The first thing I do with any computer is max the RAM out.
Also, iFixIt.com has video tutorials on how to do things like change RAM.
Why would you need anything faster? Did this upgrade to all 3 family BMB's, one 2.2 and 2 2.4's. as well as the one new Uni-body MBP, OMG talk about quick. BTW the price of that 4Gb stick of OWC Ram just came down 50%, hence I jumped.