I wouldn't hold my breath for a 5D MkIII. I'd say it's probably at least a year away, maybe longer.
A tilt/shift lens can be used in very creative way to move the plane of focus around, either to attract attention to an object or to get all of it in focus when shot at an angle.
As for a zoom, depends on what camera you get. For full frame I'd look at the
EF 24-105mm f/4 L IS USM. Good lens, good zoom range, good image stabilization. This lens also works well on a crop sensor camera and it's a lens I use myself so I can recommend it.
If you need something for a crop sensor camera and still want wide angle to short telephoto capability you might look at the
Canon EF-S 17-55/2.8 IS USM or if you want to save a little money and don't mind going 3rd party, the
Sigma 17-50/2.8 OS HSM.
If you are going with a crop sensor camera and don't need a fast lens then the
Canon EF-S 15-85/3.5-5.6IS USM is worth a look.