Pentax 6x7 or 67 is a fine camera, but there's one downside for landscape photography: weight (well, size and weight, to be honest). Lens quality is top notch, and while not exactly cheap, prices are good, plus these cameras are real tanks ... The GW690 models feel somewhat less well made, but are very sturdy nonetheless. You have to look for the rather elusive GSW690 to go (somewhat) wide-angle, though - the GW690 give you a 35mm equivalent ...
Before going Pentacon (that's my system of choice), I'd suggest assessing your usual shooting conditions - if you're often shooting in cold and humid conditions, the cameras are prone to failure. I love the style and operation of those cameras, but using them in cold weather has to be discouraged. Access to lenses is good - and the Flektogon 50mm f/4 (26.5mm equivalent in the diagonal) is a fantastic lens and very affordable. For landscape, I'd get the Flektogon and a Biometar 80mm f/2.8 to start with; you don't need a prism finder, either (I actually prefer the waist-level finder - but the prisms are actually also quite nice). Viewfinder coverage is lacking, though; if that's a problem, you have to look elsewhere. This'll get you started for less than $500 - but make sure to thoroughly test the camera before buying. I have two working bodies (one with an expert overhaul, one without in decent working condition) - but frankly, that's somewhat rare. CLA is a must if you are serious about using the cameras.
All in all, I'd say the Pentax 67 route is the most desirable one if you can abide the weight - and are prepared to pay $1500 for a landscape setup. If size, weight and price didn't matter, I'd get a Pentax 67 II with a couple of lenses and be done.
All that said, I actually have one camera I actually carry regularily: the Mamiya 6 MF. Its bigger brother, the Mamiya 7 (II), should be one mean landscape machine (the 6 is already very good, using the 50mm f/4). You end up with a somewhat smaller setup, especially if you forego the tele lenses. But these cameras are so sought-after that they'll set you back at least $2500-3000, and that's not counting the wide-angle lenses ... The 6 MF is a little cheaper.
EDIT: As usual, your post got me looking around
I'd say that the best value is in Mamiya and Zenza Bronica system cameras - but they *are* bulky. However, around here, a Mamiya RZ67 with wide angle lens can be had for considerably less than $1000 - and that's with *a lot* of extra equipment. Auction prices are lower. And the Bronica models are even cheaper.
M.