Why not keep your current speakers and purchase a new reciever? Most recievers allow you to designate which speakers are small/large/not present. So for the fronts, set them to "Large", the center and surrounds set to "Small" and just have the sub disabled. That way your fronts will out put all the bass without drowning out your rear speakers.
Well, that's what I'd do anyway. Here's a couple recievers I've been eyeing at newegg:
Pioneer VSX 818-V-K
Yamaha HTR 6130BL
Yamaha HTR 6140BL
You might check places like Circuit City, Best Buy, etc- for some good recievers. I'm betting your speakers are fine, you just need a good reciever to power 'em.