What if I didn't go the HTIB path?

$600 is really tight if HTiB's are not a consideration (HTiBs are cheaper, so by definition, eliminating them means you'll either wind up spending more now, or piecing your system together over time).

How big is the room?
Will this be 5.1 or something else?
Does the $600 include a Blu-Ray player and/or TV?
If not, what make and model TV player do you currently have?
What about other sources - game system, cable box, etc.?

Most likely, a decent, HDMI-capable receiver with enough inputs to support a growing system is going to eat up at least half your budget. Depending on the size of your room and your expectations, $300 is not going to be enough for a 5.1 speaker setup.

I used to recommend the Energy 5.0 Take Classic system ($200) for folks on a limited budget, but it looks like Energy is no longer offering that set - I can't find any reference to it on their website.  Dayton makes some capable subwoofers in the $100 range that are great for the budget-conscious, too.

Most likely, your best bet will be to approach this piecemeal.  Start with a receiver and maybe a pair of main L/R speakers.  Later, expand with a matching center and/or subwoofer.  Finally, get the surrounds last.  This approach is the best way to maximize the value of the system.

Particularly with speakers, a quality set of speakers will outlast every other piece of equipment in your system - guaranteed.  Therefore, many people who are serious about home theater put most of their budget towards speakers - as much as 2/3 of the total system (including TV, etc.)