Gamespot has a good "Rumor Control" article up dissecting the rumor that Sony is set to launch a 120 GB or 160 GB PS3, with the DualShock 3 controller, in lieu of the current 80GB model, which they would phase out.
It seems likely that this will occur within the first half of the year, perhaps near the launch of GTA IV, so what to do? Wait to buy the new version or strike now?
First, there is no word yet if the new (rumored) model will have backwards compatibility with PS2 games. Currently, only the 80GB model has that capability, as explained here, via software emulation.
Second, we can only assume that the price point will remain at $499.
Third, this rumor may not be true. The 80GB model has only been in service since Oct., 2007. That would be an awful quick turn around to replace it.
Fourth, you'll have to factor in the cost of buying a stand-alone DualShock 3 controller if you go with the current 80GB model once they hit stores this spring.
My advice is to wait and see. Once the announcement hits (if it hits), and you are armed with all of the information, you can strike quickly and grab one of the remaining 80GB models before they sell through, or wait until the new model arrives.
We'll keep you up to date on any action on that front. In the meantime, start saving your money (hey, you're getting $600 in tax rebates, right?).