Canon 16-35 F/4 covers a good general purpose range, is weather resistant with front filter, takes standard filters.
Rokinon 14 mm F/2.8, Good for casual astro photography. Very wide coverage, useful when you need to be right on top of the foreground elements, more so than the 16-35 Canon. Does not take screw on filter w/o investing in a cumbersome setup.
Since you've not stated an application, its hard to recommend anything in particular.
Venus optics has some very interesting lenses.