Medium Format, best bang-for-the-buck would have to be the Hartblei 1006
Takes all Pentacon Six lenses (like the Zeiss Flektogon 50mm f/4 ~$100, Biometar 80/2.8 ~$50-100, Biometar 120/2.8 ~$100-150, Sonnar 180/2.8 ~$100-300, Sonnar 300/4 $200-300), all Kiev 60 lenses (and Kiev 88 / Hasselblad 1000/1600 lenses via a $10 adapter) including the Zodiak/Arsat 30mm f/3.5 fisheye ~$1-200 (which is nearly as good as the Hasselblad $3000 fisheye).
It's better than the Kiev 88CM because it offers mirror-lockup, takes NT backs (which are back/forwards compatible to Hasselblad backs), and does double-exposures. Can take 6x6 and 6x45 film backs.
(I'm getting a 1006 when I can afford it).
Step up is the Mamiya RB/RZ67, and Pentax 67, I haven't experienced either but the Pentax 67 45mm is apparently a very good landscape lens (from what I've heard, the RB/RZ 67 is more a studio camera).
Down a size, why not just stick with Canon EF lenses? An EOS 3 will set you back $150-250 shipped, a 1V up to $400-500. I'm addicted to my EOS 3 only a few days after getting it. AF craps all over my 7D, especially with spot-metering-linkage and eye-control AF (won't help you with Zeiss lenses though, but the build quality on the 3 is as good as a 7D)
Down a size again, for a cheap rangefinder, check out the FED/Zorki line of soviet-ripoff-leicas. Can't go wrong for $25, if you get a good one you can stick on a Leica LTM39 lens for much better IQ...