Depends on what you want it to do and if the rest of the system will get the best from the upgrade.
If your pc is 3-4 yrs old, and you're into games, at that price a 6600GT would be my recommendation
Try Ebuyer click here
search for 6600GT AGP. There's a couple of Gainward cards for just under £90.
Note: you'll need a reasonable power supply with a spare molex connector to plug directly into the card (or use a splitter cable)