I guess just go in and do some auditioning.
If this is HT, make sure you get a nice center channel. If you're going to skimp somewhere, do it on the surrounds.
Get a cheap receiver. See if they have a floor model for a good price. I got a Pioneer 1014 for $287. $200 to $300 range is probably a good bet.
Pioneer 515/815 would be a good idea from BB
Sherwood for super cheap at CC if your speakers budget ends up on the high end of things
Others at CC
Panasonic XR-55 (says web only online, if you can get one for under $300, that would be a nice one to get)
Onkyo 303/503
If this is mostly music, concentrate on the FR and FL speakers.
Listen to them if possible. If they have a demo room, bring in some music you're familiar with and see what sounds good to you.
Check out Infinity Primus series at CC
Athena, JBL, Klipsch at BB
(and whatever else they have)
Remember that you can add to the system later on.
For example if you get a 7.1 receiver and get a 5.1 set with cheaper bookshelf speakers now, you can add something nicer from the same brand later on and move those to FR/FL duty.
(for example if you wanted to do JBL e series from best buy you could get some e20/e30 bookshelf speakers for now.... oh great... BB just went down for me. oh well)
Don't worry about buying a sub that matches the brand of the speakers if you like a different brand better.
The front three speakers are important to match. Surrounds can be whatever if you can get a good deal on something else.