MNPoolDreamer:
There are several great suggestions in this thread. I would present these to the HOA board (with a witness present, if possible). If the board will not approve any of these suggestions, I would take 'em to court. Though it may take some extra effort, I'm sure you could find an attorney who will work with you. Show the judge all of the suggestions you presented along with the pictures of other violations in the neighborhood. You hate to pit neighbor against neighbor, but this is what HOA's often result in. Anyway, this approach would show that you have made a good faith effort to work with the HOA board and that they are being unreasonable. I would also research state/local regulations governing HOA's. You may be able to get the whole thing dismissed on procedural grounds. It would pay to do your homework.
Regardless of how this winds up, at the end of the day you would show the HOA board that you will not be intimidated by them. Yes, you may not make any friends on the HOA board, but they will secretly respect you more and will likely move on to easier prey in the future.