Since it's been pretty nasty in most of the country weather wise, protecting expensive camera gear from the elements is probably on most sports shooters minds. There are a couple of companies that make rain covers for camera's and lenses such as Kata, Aqua Tech, Tenba, etc. Some are inexpensive and some are not. The best way to choose is to see the cover in person and see if you find it easy to use the camera, see through the lens, work all the buttons, etc. Keeping dry is important but if you can't get the shot you might as well just come in from the rain, unfortunately you probably won't find a good selection in your local camera store, they will usually carry just one or two brands. I have the Kata system, it works okay but I've found it a bit bulky, so I don't always carry it with me since it doesn't really fit in my bag very well. I also find it a bit difficult to shoot with, hard to see through the eye piece, so it has to be pouring for me to bother with using it.
ThinkTank has come out with a rain cover that looks very promising. Reviews have been good and it has a ton of neat features that show a photographer was actively involved in it's design. I use the ThinkTank modular belt system and have been really pleased with the it, every bag has it's own rain cover. Their new rain cover system looks a lot less bulky than the one I'm using and I like the fact that there is a place for the camera straps. Here's a link to the ThinkTank Hydrophobia . If you are looking for a roller bag, The ThinkTank Airport Series seems to be the bag of choice among most pros.
As you may have guessed by now I am a big fan of ThinkTank bags, they're well made, well thought out and their customer service is second to none.