Possible lenses to look into for your interests: a longer telephoto and an ultrawide. For wildlife, it helps to have access to longer focal lengths. Does your 70-200 provide you enough reach, or do you find yourself wanting something longer. If you often find yourself wanting something longer, something like the 100-400 might be the ticket. A shoulder strap (i.e. Blackrapid) makes carrying longer lenses easier and more comfortable.
Landscapes... it depends on where you can stand and how far and large the subject. UWA lenses stress foreground elements, so it does require thinking about composition differently than longer focal lengths. Assuming you are using a APS-C camera, you're starting at a FOV equivalent to 29mm on full frame. Something like a 10-18 would give you a lot more flexibility on the wide end.
I know you didn't mention portraits in your interests, but a fast prime gives a shallower DOF look that your current lenses can't reproduce. Lower price options like the 35 f/2 IS or the 50 f/1.8 would give you a much different look than the f/4-f/5.6 options you currently have.
