Well, if you can find a Audigy 2 ZS brand new collecting dust somewhere, it sould be for a very excellent price. It may not be the latest and greatest, but it will do fine for gaming and will be much better then onboard.
There are also very cheap Audigy cards, but I have no idea how good they are. They seem more like OEM cards then retail cards.
Your final recourse is to just get a X-FI based card.
One final note, if your using Vista, Creatives driver support seems to be hit and miss, so you may have to go with a card made by other companies, but then you run into the problem of the card supporting only up to EAX 2. Lots os the top dollar cards with EAX 2 are still software based FX mixing.
Kinda a bad time to be upgrading sound. Still seems to me like either your upgrading for gaming, or your upgrading for quality. But if your running Vista, your better off not upgrading and just waiting to see if driver support improves.
Btw, I just remembered something else. Does FEAR let you set how many sound channels to use? Like 16, 32, 64? If it does, try reducing it to the lowest amount. I just remembered that alot of software based cards also use the cpu for mixing all the channels as well.