It's a bit of a challenge. The 17-55 will give you the best image quality of the choices you list. But, if 55mm is not long enough then that's not the right choice, because the primary determining factor in lens choice should almost always be focal length first. Still, 18 MP allows a lot of freedom to crop, as long as you're not making very large prints.
I think you would find that the 100 L would be often too long, and definitely not allow sufficient flexibility for family events. A zoom is usually a much better choice in those situations, unless you are shooting with more than one camera.
In your place, I think I would go with the Canon 17-55mm f/2.8 IS. Personally, I think it is the best general purpose zoom lens for a crop body. It also works very well combined with a fast telephoto prime, such as the 85/1.8, which makes a very nice portrait lens on a crop body.
You could also consider the Tamron 24-70/2.8 VC. However, I find that 24 mm is usually not wide enough indoors on a crop body. It's not even wide angle, technically that lens is a normal to telephoto zoom. Indoors, you can always crop, but often you cannot back up.
Good luck with your decision!