Do you already have a receiver? If so, what brand/model is it?
If you are looking for an entire system, including receiver, then take a look at the Onkyo HTiB systems, The HT-S5500 is a 7.1 system and the HT-S7409 is a 5.1 system and both are under $600. I don't have any of these systems but I have heard similar systems. They aren't too bad for HTiB systems but going with a separate speaker package + receiver/pre-pro/amplifier is generally better. I would recommend HSU Research or even Emotiva speakers but those are out of your price range, unless you start with a 2.1 system and build onto it with their surrounds. Emotiva has huge discounts on their speakers right now along with free shipping within the USA. Their X-Ref 5.2/4.1 package of 5 speakers is currently at $847. Regularly $1327.
Denon AVR X7200WA, Emotiva XPR-5, Emotiva XPA-7, Sony XBR 75" 850C, Oppo BDP-103D, Roku 4.
DefTech BP7000SC (L/R), CLR3000 (C), SM55 (FH), UIW BPZ/A (SB), UIW 75 (TM).
JBL L7 (Sur), EoSone RSR 350 (RH).
PC 2.1 setup. Emotiva Stealth 6, SVS SB2000 sub, Emotiva DC-1 DAC.