For wide-angle shots (even wider than the 18mm from your kit lens), I would recommend the EF-S 10-22 mm lens by Canon. This lens is real wide (16mm equiv. at widest setting), and will give you amazing full-arena shots. However, this won't be as effective for capturing specific subjects.
I would also recommend the EF-S 17-55 2.8 by Canon too, however, this range is basically the same you have right now with your kit lens. The advantage you get with this other lens, is sharpness and better low-light capability. It's a great investment.Cons: it's expensive.
The EF 24-70L 2.8 is very expensive and out of you budget. It is a great overall lens. Wide enough and tele enough.
My ultimate recommendation would be the EF 70-200L f/4 lens. This lens is around 600 bucks and will give you perfect reach for sports, it is somewhat fast for available light photography (although you will need to crank the ISO a little), but it's a great lens overall. It is sturdy, well built, keeps constant aperture (f/4 @ 200mm is pretty good), and is a great investment in the long run. Plus, it's the most inexpensive L lens by Canon.
The f/2.8 version is pretty good as well, you get one extra stop in aperture, but it's twice as expensive.
Make sure you get a tripod though. This makes all the difference. A cheap, plastic tripod is infinite times better than no tripod at all.
1) Always shoot RAW, there's no excuse for not shooting RAW in an SLR.
2) Use tripod to avoid camera shake when not using a stabilized lens.
3) Keep your camera @ ISO 800 to get clear pictures. If you need to go to 1600, then use it (just), but definitely do not use ISO 3200.
4) If you need a faster shutter speed, then set your exposure to -1, this will give you twice your shutter speed, and -1 exp. is easily fixed in post-processing. Do not exceed -1 though.
5) Keep your maximum aperture while shooting sports.
Hope this helps!