I think the point that a single 9800GT isn't really powerful enough to NEED more than 512MB is one that should be considered here (and a GT220 w/1GB of vram is a bit of a joke ... that card would be better matched with 256MB).
By the time that you get into settings challenging enough to actually require more than 512MB, the core is going to be lagging anyways, thus such settings are not likely to be made playable just by having 1GB instead of 512MB.
Getting the 1GB version would make sense if you were getting two of them for SLI, but for a single 9800GT setup, 512MB is perfectly sufficient, it's well matched to the power of the core.
It's tough to beat the deal of a brand new 9800GT for $50, and it'll be nice upgrade from the GT220, for sure. I'd say go for it, based on what you play currently and needing to do it tonight.
However, if you could wait a bit and spend a bit more and have access to NewEgg.com, the best deal going right now on new gfx cards is the Sapphire (ATI/AMD) HD5850 Extreme for $139.99. It's a very powerful card for only costing $140, has DX11 capability, a full gig of vram, and is probably three times more powerful than a 9800GT....
5850 is a much more suitable card for gaming at 1080p resolution than a 9800GT to be honest, and should last you a few years instead of being outdated from the start like the 9800GT is.
There's some nice deals (some just over $100) to be found on 460GTX 768MB cards ATM as well which is also a very nice DX11 card ... not as good as 5850, but still solid, a HUGE upgrade from GT220, and significantly faster than a 9800GT.
There's also some ATI/AMD HD5770 cards still around, and they're down to the $100 range nowadays, and are also DX11, and well worth considering.
Edited by brettjv - 5/6/11 at 2:16am