Landscape can be shot with any focal length, some of the more interesting shots are actually had at 100mm or longer. I like my 50mm f/1.4 for many shots too, at f/8 it's pretty good across the whole frame on a 5D2. Combine that with the DLO feature in their DPP software and you can create some seriously sharp images with it.
But if you're looking for wide, and I know what you mean, sometimes a super-wide shot makes a very interesting composition, then the 17 & 24mm tilt-shift are fabulous options on a FF. I'm still waiting for a Canon FF body truly worthy of those lenses for my kind of shooting tho so I don't own them, just want to.
The 17-40mm f/4 L is a nice range but the lens is terribly soft in the borders and corners on full frame even when stopped down. Need to use it at least f/8 to f/11 and it will still disappoint at 17mm in the corners. I spent most of my shots with it in the 20-24mm range when craving wide landscape scenes, use 17mm when there's nothing with texture in the corners.
I haven't used the 16-35 L, it's a lot more $ and does chart a little better for optical performance in borders and corners if that's the range you're after.
I don't think any of Canon's current wide primes perform well in the corners either, even the L's aren't stellar. The 16-35mm zoom would be preferable.
24mm f/1.4 L II is not bad but at that price consider the cheaper Voigtlander 20mm... or see paragraph below:www.photozone.de/canon_eos_ff/514-canon24f14mk2ff?start=1
As long as you're spending, Nikon's 14-24mm f/2.8 on a D800e makes the ultimate super-wide-zoom combo. That lens is a benchmark for sharpness in that range. Has its other foibles tho.
I like the old Nikon/Nikkor 20mm f/2.8 AI-S on my D800/e when I want wide performance.
And I can use it on my Canon bodies with a cheap adapter ring. I like it on my IR-converted 50D.
Tokina also makes a 17-35mm but it's even worse than Canon's 17-40mm.
Samyang has a very crisp 14mm prime but it's got a fair bit of center distortion, workable for some scenes but nothing with straight lines in the borders.
I haven't explored Zeiss and other premium 3rd party options enough to comment. Perhaps others here have.