You mentioned a zoom would be handy but not a budget. I found the midrange 17-85 IS was a good companion to my old 350D. That was until I dropped it in a glacial river. Be aware it's not environmentally sealed, neither is the 350D but it survived. I felt it's optical quality matched the price and weight etc, but it didn't exceed it. One small gripe is that you have to pay extra for a lens hood and soft case on a prosumer lens. I didn't replace it as I changed systems. I still have an EF 17-40 F4 which I am very satisfied with optically, but it comes up a bit short for me. It's mated to the 350D and lives in the car, I use it as a point and shoot setup.
I have never used it, but the EF-S 17-55 would be in the focal length ball park. I have a Nikkor 17-55 DX 2.8 lens and find the focal length very good for landscapes. It's not often that I have to resort to something wider. I'm quite new here but I have the impression there are a large number of Canon users who will have some good opinions for you on that lens. The focal length looks good, but in view of Canon's product portfolio I could imagine it's a controversial lens.