First thing you should do, before buying any type of strobe, is check out the Strobist website. A lot of great information can be found there. Infact, just about anything you want to know about shooting with strobes can be found there along with contests and assignments. A great resource.
Since I shoot sports a lot, I thought I would just scratch the surface of using strobes for sports. We would all love to have that perfect light outdoors, but there are times we need a little extra. A good example is night time football. You can only get away with using flash with football in high school and bellow, but thankfully, most college and pro venues have enough light that you do not need a to add any light.
With football, one thing you want to avoid is on camera strobes. With long lenses, having your strobe on camera will give you very bad red eye. There are ways around this though. A flash bracket for your camera, or one that mounts on your lens tripod ring is a great way to do it. When I shoot with a 300mm lens, I am always using a monopod and I mount two, Vivitar 283 strobes about 16 inches bellow the camera on the monopod and fire them wirelessly. By having the strobes set to 1/4 power using a Vivitar VP-1 power adapter for the 283's, I get good recycle times and a lot of light being thrown onto the football field. I have talked to another photographer who uses Vivitar 285's in the same way but he has one of the strobes set to around 50mm (on the head of the strobe) and the other set to a telephoto setting (I believe 100mm +/-). This gives him one flash that is illuminating a wide view and one giving him a throw of light further away. I have also seen photographers set up a light stand on the sideline with a studio strobe or two or three and even seen strobes mounted up in the bad high school stadium lights. Another fun way to shoot with a off camera strobe is a strobe on a stick. Mount your strobe and pocket wizard on a monopod and have an assistant stand about 10 yards from you, following the action with the strobe and when you fire, bam, nice 45 degree side lighting. It does not work perfectly, but it is pretty fun when it does.
The above set up will work with just about any field sport. LAX, football, soccer. But do not, I repeat, do NOT use this with baseball. Umps, coaches and players do not want a strobe going off that could distract someone as a ball is flying at them at 60mph or faster, and you do not want your strobe going off at the instant a play is made that blinds the umpire so he can not make a call.
Now for indoor sports like basketball, the set up is different. Some high school's do not allow strobes or on camera flash. Check first to see if it is ok. And do not use on camera strobes on the baseline. Basically, you want your strobes out of a direct line of site for the players. I mount my strobes about 20 feet in the air at the corners of the court. I have the strobes set to a wide angle covering from the baseline to about mid court. You want a strobe that recycles fast and puts out at least a guide number of 200. The Vivitar's are fine for this, but you may find that studio strobes will be a better option. There are a lot of discussions on various forums online about what strobes to use and how to use them. Bounce, direct, sports reflectors, ISO's, etc. Best thing to do for you is practice practice practice.
Now. After going over this, you are more than likely thinking, "That's great, but I need fast shutter speeds to freeze the action, and my flash will only sync at 1/200th of a second." That is all you need if your strobe is powerfull enough and has a fast duration. Over powering the ambient light is key here. If you over power the ambient enough, your strobe is the main light source. And if you have a strobe with a duration of 1/2500th, then even though your shutter is only set at 1/200th, you are capturing the action at 1/2500th of a second. Think of it as your strobe is now your shutter. Take an exposure reading for the strobe, set it to your camera and you are good. If ambient light is 1/125th at 2.8 and your strobe gives you a exposure of 1/200th at 5.6, then set your camera to 1/200th at 5.6 and you are good to go. Images will be captured at 1/200th but because your strobe is doing the actual work of the shutter, it will freeze the action and make it apear that you used a super fast shutter speed. So, using a hand held light meter is important. With my Minolta Flashmeter V, I set the camera shutter speed flash sync, which for my 1D is 1/500th and 1/250th for my 1D Mark II, and I start with an ISO setting of 400. I then take a reading from the basketball court of with the strobe. For basketball, I shoot for around a F4-f5.6 reading. If I get that, I am good to go, but if I get an F8, I will drop my ISO or if I hang around F2.8 I will increase the ISO to 800. Set your camera to what your light meter says and you are good to go.
So, when buying a strobe (flash), decide what you need it to do, what you want it to do, and research what will work with your camera and what will fit in your budget. Canon makes speedlights that scratch $400 - $500 and Vivitar makes flashes around $100. Canon's will be fully compatible with their cameras and have all sorts of features, where Vivitars will be a basic full manual strobe.
My final advice was aready touched on. Read Strobist.com