There seems to be two major "philosophies" when it comes to Join pages. (I assume you are referring to pages you post yourself or do you mean 3rd party forms, which you have less control over?)
Lots of text (sales pitch) vs. little text. I go with little text, lots of pictures, and few join options. These are on the pages I myself host:
http://www.chubbyblondy.com/join.html
Very simple and clean, with unique buttons.
When it comes to forms hosted elsewhere (like with CCBill) I use custom forms I designed myself and A-B tested.