The best lens for landscape photography, hands down, is not a zoom. For your Nikons and Canons, get a 24 mm perspective correction (PC) lens. They are expensive, but their control over depth and perspective is unmatched. They are also what you need for good architectural photography. If you insist on a zoom, there is a little rear lens attachment made by Novoflex and Zork, I think, which allows some tilt. Alternatively, any good 18-200/250 mm general purpose lens is OK if you do post processing and can use one of the photo software routines which merges images made at close, midrange, and distant focus. While you are at it, also get an HDR (high dynamic range) image routine. You will be thunderstruck by the quality of your images! Check OP for details.