Lots of different options, any idea on what kind of connectivity you need? (Hdmi, network, connecting a cable/sat box, dvd/blu-ray, CD player) Is internet radio or streaming content important to you? How about video/audio processing?
Yamaha is a good brand, but their audio calibration isn't as good as audyessey.
Onkyo packs in a lot of features, but unless you want to invest in some fans to sit on top, or maybe raise your budget a touch I wouldn't necessarily push you in that direction.
Pioneer's are good, but known to be less user friendly than other brands and their audio calibration software is also not as good as audyssey.
Denon makes pretty good stuff, fairly user friendly as well.
Marantz makes rock solid stuff, I really like their gear, but you lose some brand name features (not that you don't necessarily get the same features but they won't have the big name stickers)