I'm just one of the regular helpers around here. BTW, it's "jam" :-)
There are plenty of good AGP cards still available...it all depends on how much you're willing to spend & how good your power supply is. Many AGP gaming cards are power hogs so having a decent power supply is very important.
I'm gonna have to disagree with 1stepbeyond though...SiS video cards flat out sucked. Notice that you rarely hear them mentioned. The two big players are nVidia or ATI & those are the only ones you should be considering.
When selecting a card, it's important to look at the specs. 8X AGP cards are backwards compatible with 4X AGP slots so that shouldn't be an issue. The memory used on the card is very important though. For gaming, you should avoid cards that use 64-bit memory...go for either 128-bit or 256-bit. The type of memory used is important too...from slowest to fastest - SDRAM, DDR, DDR2, GDDR2, GDDR3. I suggest you look for a card with 256MB 128-bit GDDR2 memory. It should also support DX9.
I did a quick search at amazon UK & came up with this ATI Radeon X1650Pro. You don't need 512MB on an AGP card, but it certainly won't hurt: