i second the suggestion of the little isolette for fun. i recently purchased one on ebay for very little and love it. i throw it in my purse and go. because it folds no worries about the lens.
this article is the reason i decided to get one. the author's serious cameras are mamiya rb and 645. he speaks about different folding cameras, lenses and shutters: http://www.cleanimages.com/Article-M...YourPocket.asp
i have a mamiya 7 with 80mm and 150mm lenses. i love it, tend to use the 80mm most. i use the RB67 for studio work. i bought the
7 and both lenses from KEH used some years ago. all in excellent working condition. i wouldn't hesitate to buy from KEH again. all my
experience with them has been good.