Used Cameras

[Groupcaptainbonzo]

As you will have seen the main thing with Landscapes is the lens.Any of those you mention will do a great job in conjunction with the right lens for the circumstances which prevail at the time. The only thing I have to add is that some landscapes will require you walking a long way over difficult terrain. If you are planning this then a small light camera with a good quality lens, that retains all the versatility of the main DSLR bodies would be important. As such the 400d (Rebel XTi) is definately worth a look. With (If you can afford it) some "L" series Glass stuck to the business end.
(I am sure that Nikon and Olympus will do something similar if you lean in that direction. Although I have never used Nikon, and I've not used Olympus since my old OM3Ti got lost (Long pause while I start crying .... AGAIN).