What Keeper League Rules Have You Used?

[Dutchrudder]

So I'm in a league that I don't really care for all that much, but a friend of mine runs it and I don't want to quit. I was thinking it may be fun to turn it into a keeper league starting next year, but I'm not sure what sort of rules go into it. Have you ever played in a keeper league? What sort of rules did you use regarding the players and what qualifies them to be kept for the next year? What draft picks do they cost? Just curious what sort of ideas are floating around out there, I have an idea of what I want to propose but I would like some more input first.