I'm asking this question since my computer (As you may guess from the title) uses an AGP slot, which is pretty clearly old, but the computer itself functions well, and I'd rather not get a full new one, or mess around with new motherboards and such, until I really need to. However, there are some games coming out/that are already out that are a bit too much for the current card. (This s to explain the question, and avoid people arguing that I should just get a new computer. This one does have quite a lot of RAM, hard drive space, processor power, etc., the graphics card is the big weak point.)
I've checked out a few of the expected places, but haven't found much. I'll be sure ot check out some more, but extra information is always useful. 
