With my 10D I got both the 17-40/4L and the 70-200/4L. They are both superb. Since I do almost exclusively outdoor natural light photography, I have never wished for a faster lens (or the added weight). I probably used the 17-40/4L for 95% of the images I took with the 10D.
I eventually moved up to a 5D (full-frame), and those two L-lenses still do fine. But I have recently indulged in the 24-105/4L IS, which has become my 90%-of-shots lens, not for the image quality but for the image stabilization, which is worth a lot to me.
Do think about how much hand-held work you do (go for IS if there is much of it), and consider how much indoor/dim light work you do (go for a faster lens if you need that). Also consider how wide you want: for me, 17mm was great on my cropped 10D, but 24mm is (barely) wide enough onmy full-frame 5D. Of course, YMMV.
Good luck with the choice.