I got the 17-40 F4L when I bought my 30D, and for quite a while it was my only lens. I still use it for about 75% of my photography, mostly landscapes and buildings. A lot of people dismiss the 17-40 on a crop body, but at it's wide end it's the equivalent of 28mm, which in my book is pretty wide. For times I need wider, I now have the 10-22mm EF-S.
However, if I was starting today, I would give the 15-85 EF-S serious consideration, since it looks like an ideal combination for most work in a crop sensor camera.
I've not seen a side by side comparison of IQ between the 15-85 and the 17-40, so I'm not sure how the resolution of the 15-85 holds up compared to the 17-40.
I've always found the results from the 17-40 are superb, really sharp with good contrast, colour and resolution, and the AF is so fast I sometimes force it to refocus because I missed it the first time.