I personally just added another 8GB of DDR3 (G.Skill Sniper to be exact) on sale from NewEgg for $72 plus a free 2gb flash drive. I haven't received it yet, but now is a perfect time for a RAM upgrade.
In fact, NewEgg is having a 15%-Off Desktop memory sale as we speak right now, so if you find something you like, I'd go ahead and order it as soon as you can.
I could list page after page of recommended memory, so I'll just say this: You can't go wrong with G.Skill, Corsair, Mushkin, and Wintec. I'm really sorry to them, and they make great power supplies, but I can't really recommend OCZ's memory after seeing their failure rates. Just pick something you like that has good reviews and you should be okay.
Hah, yep, so do I. I also recall paying $156 for a 4GB kit of Corsair Basic DDR3-1333. And that was pretty much exactly one year ago... man... I just couldn't have waited one more year to build this.