I recently took the MF dive a few months ago and regret nothing about it. I'll throw my 2 cents in and recommend a mamiya 645 system. The quality is excellent and it is one of the most prevalent MF systems around so you'll have less of a problem finding accessories and equipment at a good price. Interchangable backs are also something I would never be without when considering a MF system. (avoid the newer 645E if this is something you want) Some of the early model 645's also lack this feature. Being able to rapidly swap film midroll alows for great flexibility and experimentation. The Mamiya RB's, RZ's and other larger MF SLR systems are desirable for the even larger negative size but they are considerably more expensive (budget-dependent of course) and higher maintenance due to their leaf shutter design. The lenses are considerably more money and their shutters need to be periodically adjusted in order to be 100% accurate. The Mamiya 645's electronic focal plane shutter will pretty much stay accurate for eternity if treated with reasonable care. Either way take your time looking around and consider your needs and uses before committing to a system.