I'll add my vote for the 17-40 f/4L.
It's a superb lens that will be even more useful if you ever want to move to full-frame. It's also weatherproof.
With the good high-ISO performance of the latest cameras, a fast lens isn't as important as it was. After all, f/2.8 to f/4 is only the difference between ISO 100 and 200. An f/2.8 lens will also be larger and heavier (assuming the same image circle), and more expensive.
I love IS but it isn't so necessary at shorter focal lengths, and on a tripod you're supposed to switch it off (although I don't). It comes into its own above about 100mm, and if you can run to it I'd strongly recommend the Canon 70-300 IS. Longer than 300mm and you're really into big bucks for something decent, and you may need a yak.