does anyone know what the best Gcard i can get with agp 4x slot?

Compatibility
Compatibility, AGP Keys on card (top), on slot (bottom)

AGP cards are backward and forward compatible within limits. 1.5 V-only keyed cards will not go into 3.3 V slots and vice versa, though "Universal" slots exist which accept either type of card. AGP Pro cards will not fit into standard slots, but standard AGP cards will work in a Pro slot. Some cards, like Nvidia's GeForce 6 series or ATI's Radeon X800 series, only have keys for 1.5 V to prevent them from being installed in older mainboards without 1.5 V support. Some of the last modern cards with 3.3 V support were the Nvidia GeForce FX series and the ATI Radeon 9500/9700/9800(R350) (but not 9600/9800(R360)).

It is important to check voltage compatibility as some cards incorrectly have dual notches and some motherboards incorrectly have fully open slots. Furthermore, some poorly designed older 3.3 V cards incorrectly have the 1.5 V key. Inserting a card into a slot that does not support the correct signaling voltage may cause damage.

There are some proprietary exceptions to this rule. For example, Apple Power Macintosh computers with the Apple Display Connector (ADC) have an extra connector which delivers power to the attached display. Additionally, moving cards between computers of various CPU architectures may not work due to firmware issues.

Google search an ATI radeon. (Or go to Best Buy :)But pick carefully, some cards will say 4x/8x but onyl have an 8x connector. And better is kind of a loose term, it depends on what your using it for. WoW would probably run fine with a mid-grade card. But if you're into flash creation, Photoshop and running multiple programs at once, you may want to go a little further up the chain.