obscbyclouds offers sound advice here by getting out there and listening to a few different types of speaker manufacturers. Speaker preference is very subjective, so while one person might prefer the sound from a couple of brands of speakers, another listener might prefer others that may be similar in build quality, specs, pricing, but completely different in the type of sound its able to reproduce.
Try not to limit yourself to just brick and mortar stores as well, such as Best Buy and Circuit City. Unless you're in a very remote location, there's typically quite a few audio dealers around that can work with you on pricing. Also a consideration would be one or a few of the internet direct companies. There's lots to choose from nowadays and many of them are discussed here and other HT forums. One upside to a few of these companies is that they allow a 30-45 day money back guarantee so you can try them in your listening area, which ideally is where you'd want to demo them. the downside is you'd be out the return shipping, so large towers would be a serious consideration before doing this.
Lots of options though, I would suggest going the L/C/R replacement and using existing surrounds for the time being. You'll get the best bang for your buck going this route. If I were able to travel back in time to when I first started actively making my audio equipment purchases, this is surely the way I would've gone.
Then again, if I could travel back in time, that might be a little lower on the priority list behind a few other things...
-TD
