Hard to go wrong with that setup ... yet, some thoughts.
I'm not sure I see the point of a 50D over, say a 40D or even a 30D.
Our photography is quite close, as I shoot mostly MMA events (ridiculously fast people in a ridiculously dark environment) and the odd camping/4x4 trips.
I went with a 40D simply because I wanted the better ISO management and faster burst compared to a 30D. I did not see the point of a 50D, it wasn't enough of a step-up to justify the extra cost.
Thus far I've rented at least a dozen lenses ... and am still unsure what I want to buy! hahahaha
As for glass, I've used the 17-55 last week (rented it) and I was not impressed by the build quality. The zoom mechanism required uneven strength, with hard spots here and there. The lady said it was normal ... yet it was insanely annoying. Picture quality was fine, it just annoyed me every time I touched it.
I'd much rather go for a 17-40L (f2.8)
The Canon 70-200 is the big daddy, but remember there's also a Sigma 70-200 f2.8 (no IS). I used it for a weekend and was pleasantly surprised, fast AF (not quite as fast as the Canon though) and very good image quality. I wouldn't hesitate to buy it and save 1000$ in the process.
You still don't have a wide angle. I tried the Canon 10-22, which I liked very much, except for the high aperture rating ... kills it for me and my pitch dark events. OTOH, Tokina makes an 11-16 f2.8 which looks promising, and it's cheap @ 599$CDN over here.
For sporting events, don't underestimate the power of a good low aperture prime. I shot my last MMA event with a 35mm f1.4L and was laughing all along at how fast the damn thing was. Instant focus, gobs of light going in ... I loved it. If only I could get my hands on a 50mm f1.0.
In the end I think my ideal setup will be a crap 18-55 kit lens to beat up as a daily, 11-16 Tokina and 70-200 Sigma. Inexpensive yet there wouldn't be a shot I couldn't take. Of course there's always a way to improve, but IMO that would make for a very good quality vs price setup.