Please remember that any mention of competitors, hinting at competitors or offering to provide details of competitors will result in an account suspension. The full rules can be found under the 'Terms and Rules' link in the bottom right corner of your screen. Just don't mention competitors in any way, shape or form and you'll be OK.
If you really must upgrade, i'd say the 8800GT or GTS 512MB edition.
If you want to change then either an 8800GTX or a 512mb 8800GTS (G92 core) is within your price range. However for a 19" monitor I'm not sure I'd be greatly bothered as you probably won't see a huge deal of difference.
http://www.overclockers.co.uk/showproduct.php?prodid=GX-069-BG&groupid=701&catid=56&subcat=1009
couldnt tell you how these compare to the 8800gtx though, one would asume faster naturally