sorry, haven't looked back here since my last post.
I haven't "gone" with one yet, but am choosing between the 590 and 790 that dopple suggested. I don't have much of a room to fill, and the 590 seems to have all I really need with plenty of inputs for the right price. they offer a 6.1 surround with the 680, but it only has one opt/one coax in.
the 790 looks really nice, has better front spks and sub plus two more surrounds, ipod support (through an optional dock), XM radio compatible, 3 opt/1 coax, multiple video inputs, etc. for 200 bucks more. the kid in me wants it, my sensible side says I'm not really going to use the extras. I'm going to sit on it for a while before deciding, but from what I've read you can't really go wrong with either.
Crutchfield has a great knowledge base about home theater, everthing from digital encoding standards to types of speaker wire. I just found it last weekend, very good info.