http://www.issues2000.org/John_McCain.htm
A very broad overview of some of the stands he's taken on hot issues. Not a great site, but a start.
McCain is a charismatic guy who knows how to play to a crowd...honestly though, he's a conservative, sticks with Republicans on many votes, and will NEVER be a Democrat.
I'm not especially shocked at Chafee leaving the party...but that's just me.