If you are preparing a publication for an ACS journal such as JCIM (Journal of Chemical Information and Modeling) you can paste your references in below and click "Check" to find some common errors in formatting (your references need to already be in very good shape to begin with though or you won't find anything useful). Note that this is not a validator: it does not show whether your references are correct or in the right format. It may however show some errors in formatting. After you have checked the format, you should check the actual references.
Since the format checking is all done in Javascript, you can look at the source of this webpage to find the program. If you improve the program, I would be interested in adding your improvements here, so contact me!