I'm not sure if you're still in need of help, or if my answer has already been mentioned, but before deciding on a particular camera decide if you want to shoot 645, 6x6, 6x7 or 6x9. Personally I like the 6x6, but some people don't like the square.
If you do decide to try 6x6, I think a Bronica S2A is by far the best camera to start with; it's cheap (at least compared to a Hasselblad!), easy to find (on ebay at least) and just a great camera. You can usually buy a kit in nice shape on ebay for between $150 and $300, and the 50mm wide angle lens (roughly equivalent to a 28mm for 35mm) comes up often on ebay and usually sells for $100-$200. I think there's one for sale on APUG right now... it might be an S2 or a C; if you do think the Bronica is the way to go, try to get the S2A because it has stronger gears so it's a lot more reliable.
Anyway, the old Bronicas use Nikkor lenses; absolutely beautiful photographs, and personally, I think if you're going to shoot medium format, a 6x6 is the best way to go.
Another recommendation, if you decide not to go with a Bronica, is to get a camera with a waist level finder; in my opinion that's one of the things that make a medium format camera so enjoyable (it also isn't much fun to have to lift a heavy camera to eye-level over and over!)
Good luck with whatever you choose!