Welcome....
John is right on the mark. Look for features. Some key ones for some people are on-screen interface (a lot easier to adjust levels and such from your seat using a remote than standing by the receiver reading a small display. Automatic calibration is a big one for a lot of people (John mentions Audyssey which is well known) but most if not all of the other big name companies have that or their own version. It is a great starting point for calibrating your setup to compensate for issues with the room acoustics.
You will usually find that there are certain price points that make a difference. I mean, you will be able to drive them very nicely once you get around $500+ almost regardless of any brand. that doesn't mean that the lower priced/featured $300 receiver can't do it though, but you need to do much more research on the lower cost models because some of them are inexpensive, and some of them are cheap. You get the difference....
I've had great luck with Pioneer Elite stuff, but many others love Denon, Onkyo, etc. Stay away from any "off brand" models and go from there.
