I have tried a few of these...., but it does help some people. this one: (it is good for tennis elbow/tendinitis/lateral epicondilitis)
Band-It Elbow Brace for Fast Tennis Elbow Relief
is supposed to work the best. The gel filled ones and softer ones are the least effective, the harder plastic ones are the most effective. you want the brace to put pressure just below the spot that hurts the worst(I know its hard to do because it is so high on the top of the elbow) but the tendon that is connected to that part of the elbow runs down almost to the inner wrist near the thumb.the pain can eventually radiate all the way down, even when you are not using it...THAT hurts like hell, but that is what the proper brace can help you to avoid.
When it will help the most is if you are using a "weadeater" for a couple hours, or a chainsaw.
IMO, get the "band-it" and give it a try. If that one doesn't help, none of them will.