If you want a fairly cheap, good quality SLR, have a look at Bronica's SQ-B, SQ-A, SQ-Ai (they all shoot 6x6). If you have more money and want very good lenses, have a look at Hasselblad. As for as rangefinders go, have a lok at the Mamiya 6. It is the only rangefinder that shoots 6x6 as far as I am aware.
I'm partial to Bronica's only because i have one, but I love it and would not trade it for anything. I have an SQ or an SQ-A model and with the different backs that you can get, I can shoot 6x4.5, 6x6, 35mm and also with polaroids. It gives me lots of flexability.
It's the poor mans Hassablad, the only difference really being the name brand.
thanks for all the responses guys! Once I get a scanner to scan it I will definitely get into MF....the rangefinder seems interesting and I will look at the Bronicas too.