I've got the viewfinder-level on my 7D set to M-Fn (i think that's what it's called, the tiny button near the shutter), however when shooting landscapes i'm normally on live-view (the live-view lcd-level is easier to use, although they're both as accurate).
I've also got tripod clamps with bubble-levels (this one
), rails (like this one
), my nodal ninja
also has a bubble, and to finish off, there's also a bubble-level on my hotshoe (like this one
(The main annoyance with the hotshoe-level is that I forget that it's there, when I try to use the popup flash it doesn't work because the camera thinks a speedlite is mounted, then after 5 minutes of cursing my broken popup flash I remember to take the bubble-level out and try not to lose it. Also not sure how accurate it is).
And after all that, sometimes they still don't always turn out level, and I have to rotate/crop them in GIMP or when stitching in Hugin...