Memory prices have been dropping steadily the past couple of months, but there's really no telling when this trend will reverse itself. I bought the set Glenners linked to a couple weeks ago where it was priced $25 higher than it is now. So it could very well go down in the next couple of weeks, but there's really no guarantee.
If you can get a 2x1GB set for 70 bucks, that is an amazing deal. If I were in your position, I would buy it now than wait and risk prices going back up.
Though like Craig said, you should buy it when you really need it. If you're willing to wait a week or two to see where prices go, then by all means do so. But keep in mind that there's no guarantee that prices will continue to drop.