I don't know if you got your 3870 or not but if you can get that because you'll be happy with it, otherwise I can recommend the 9600 GSO. I used one for an older build and ran all the games I threw at it, Stronghold, Warhammer Dawn of War etc (yeah old and not that demanding I know) fine, and it cost me £30, £20 to buy and £10 for P&P. The one I used was the XFX 9600 GSO 384MB, and it's single slot as well which was even better! The 8800 is/was also good as were the 9600s which I already mentioned and the 9800s, and if your budget allows for it a GTX 260 or GTX 275 would be great! I don't know how much these fetch nowadays though.
What you have to remember is that the GeForce 210 is a weak card, it's basically the lowest-end card NVIDIA make/made. I had a GT 220 (the next model up) for a while before I got my GTS 450 (which is a good card BTW for what I do) and the 220 wasn't great. Any of the cards I mentioned above will outperform the 210 by a mile.