Lots of great answers and advice already that are worth considering.

Another simple technique that I use is from a vim feature using the [%] key. If you're on an opening (or closing) brace, bracket, or paren, hitting [%] will take you to the corresponding brace/bracket/paren. So, position yourself on an opening brace, take note of your indentation level, and hit [%]. If the brace it takes you to is not at that same indentation level, you've probably found your culprit.

It's not perfect, but it's really fast, even in a long script, and it's right often enough to make it worth trying that first.