I unfortunately don't know that many US e-store but tigerdirect.com does have quite a nice selection.
Tigerdirect DDR2-800 2GB List
Well, since the 8800 GTX has been release since a few months I'll say that the G90 series will probably cost more than the 8800 GTX upon its release. Although, computer parts are always cheaper during the summer (for an obvious reason, hence less demand). Wait or not to wait, it all depends on you. Do you want your computer now or can you wait?
If you think you can wait, then wait.
If you can't wait, then buy it now.
Hell, you can wait for Bioshock to be released if you want. The game is expected to be released in mid August (last time I checked), and I doubt prices will have raised by then. Nevertheless, if you do wait until september or november, I can almost say with certainty that some computer parts will cost more than now. (Happened last year)