I'd just get an AGP card and call it good on your current system. The next time you need to upgrade consider just getting a whole new system.
As an owner of an AGP motherboard, I had to go through this and make the decision on holding out a little longer on my current system as it still has some good life left in it. I got a good deal on an ATI X850 Pro and overclocked it and modified it to an X850 XT Platinum.
Its too bad that the the corporations decided that AGP just isnt good enough anymore. Its still more than adequate and the only thing it rally cant do is handle SLI or Crossfire.