Here's one to keep in your back pocket.
Microsoft has recently released an interactive support article (KB2993943) for troubleshooting WSUS client issues. The support page does more than just give ideas for fixing problems, it provides a walkthrough for commonly known issues, delivering it step-by-step.
When a provided step solves the problem, you're met with a Success page and asked to provide feedback. And, if you step all the way through without a resolution, Microsoft will suggest that you either use their web-based forums or call support.
If you have to step away and close the support page, you can also choose to save your current progress to come back later without having to start all over.
It's worth a look (and a bookmark): Guided Walkthrough for troubleshooting problems that relate to WSUS agents that are not reporting to a WSUS server