You mean a Videocard? There are a number of places, i personally use ebuyer.co.uk but if you aren't sure what you are doing or what you need try a Electronic SuperStore such as PC World or Maplin Electronics [UK Only]. Not sure what stores in the sates. You want atleast 128MB RAM on your Graphics card, but 256Mb RAM and 512MB would be even better, but it all comes down to costs.
What are you system specs?
