The 5D is undoubtedly a great camera. Even with a replacement much rumored for next spring, it still is as good as anything out there. For landscapes, the advantage of a full frame sensor make it a winner.

The 50/1.4 is a good lens for the money, but not what I would consider a landscape lens. Depending on your budget, the 17-40/4 and 16-35/2.8 II would be the obvious starting points. If you really need low light capabilities beyond what f/2.8 can bring, then a 24/1.4, 28/1.8, or 35/1.4 are your prime alternatives, although 35 isn't really that "wide".

I've not felt a need for an ultra-fast wide lens as I usually use a tripod for landscapes, so I stop down to get better image quality.

dpreview.com has a dedicated forum for full-frame Canon bodies. Just as you ask travel questions on FT, dpr is the place for photo crazies.