Thank you for the input.
I've been mulling over the Crop vs FF issue as well, but I think I need the higher FPS that a crop gives me due to baseball and football. With that said, does that change the thought behind the approach to which glass I go with?
well, my train of thought after reading the above would be: 1. you will be doing sports photography, but for that you will have the 70-200, so the lens you are looking for now will be just general "walk around" lens and the sports photography requirements don't influence the choice much, but 2. it means you decided you will go with crop for some time and that would make me lean towards good EF-S lens (the 17-55 if you want the best EF-S zoom, or maybe 15-85 for a bit more reach on both ends)
btw, you also mentioned shooting video... I don't, but I guess IS is helpful in many video situations... and I realize that every one of the lenses discussed here has it, I just thought ill mention it in case you would bring in another alternative later
aaand one more thing...
should I just get a 50mm prime for those situations?
yes, do it
additional to the zoom... if "just" the f/1.8, for the price, its great, it was maybe my best photo gear "investment" when I bought it having only slow kit zoom (the lens explained the concept of DOF to me
e.g. for portraits, gave me more low light possibilities, the experience of using a prime...)
Edit: I keep forgetting the new sigma 18-35 f/1.8 zoom, but you might want to look at that as well, limited range, no IS, but a f/1.8 zoom... ooone point eeeight!