Well, there are a lot of really crappy speaker systems out there in the $500 to $1000 range. And you say 7.2 setup - are you really thinking of two subs? And will the sub rest on the floor?
However, with a 50" (Panasonic!) Plasma television you don't need a system that would cost a lot more (like if you were going with a projector and 120" screen). Also, I'd definitely get a decent 5.1 system as opposed to a junky 7.1 system. That way you have decent sound right off the bat; just add two speakers later and for a few hundred dollars, down the road, you've got something good.
I think Home Theater magazine had a "best speakers" issue recently - might even have been February issue. If it is still on the newsstand, I'd pick up a copy (or subscribe, it's dirt cheap for what you get).
One option that wouldn't suck would be the 5.1 NHT Absolute Zero speaker system at $1294 list - maybe you can get it in the $1000 range ultimately.
I would also check out the speakers from Gallo and Orb - I've not heard the Orbs but it is possible you could put together something decent using their speakers. (I am familiar with their $2200 5.1 systems, but not their "micro" systems.)
I never did like Klipsch, thought they were too bright sounding - BUT, I've not heard them in at least 10 years, AND you could do far far far... faaaar worse in a "cheap" speaker and only some better.
Polk is not what they were ten years ago; again, you could certainly do worse.
A speaker I have heard and really like is the Monitor Audio Bronze series (a buddy of mine has these with his similarly sized TV and Denon receiver; for the money they are very very good and you can pay more for something else (Bose?) and get junk).
Pair of B2 speakers $400 list
Center Channel spkr $280 list
Bi Pole surounds BXMX $400, I think.
Woops, that's $1000, taking into account street price and sales tax. BUT, if you could stretch, or find these used or maybe these new and a good used sub, this is a system that would be 100 times better than most HTIB systems - you'd never tire of it (until you find $2500 to put in a speaker system).
A couple of words of advice:
Don't skimp on your center channel. It will do the most work, percentage wise, and it will give you the feeling of "being there"... or not, depending on your choice.
You can cobble together a system using good speakers from different mfrs. and have a better sounding system than any junky HTIB system. However, if you can at least match your front three speakers you will be way ahead of the game. At your price point, three front speakers that match, any decent surround pair, and a good used sub - and you will be amazed.
I'd MUCH rather have a used sub for $300 that is pretty good, and was once twice that amount, rather than a new $300 sub that is pathetic (and at $300, they all are pathetic).
Check out Audiogon.com and Videogon.com if you will consider used speakers. Sometimes you can find a complete $2200 5.1 system that is "the real thing" for $1200 there. Mfrs that I know make good sounding speakers are Mirage, Paradigm, Definitive Technology, Focal, PSB, Phase Tech (they used to anyway). Also the Monitor Audio Silver series is superior, if you can find a "deal" on them. Also Gallo's A'Diva-Ti based system is amazing, and easy to install "above ground".