I would suggest a 17-50, either canon or third-party as a walk-around lens, and perhaps a 70-200 to be able to isolate objects that are further away. The 17-50mm lenses usually deliver great quality (at least the 2.8 versions of Canon and Tamron). I use my Tamron 17-50 2.8 non IS probably 90% of the time, and I shoot a lot of landscape. If you like night photography, concider getting a tripod. They don't have to cost too much if you are strong enough to carry some weight.

Lars