What is an easy, reliable way to determine the type of container a video file uses on Windows?

What is an easy, reliable way to determine the type of container a video file uses on Windows?

There are a lot of different video file containers floating around (AVI, WMV, MKV, OGM, etc.), and I've found you can't always trust the file extension. Too often, some confused individual changed it to something that she was more familiar with (for instance, from MKV to AVI), and that can become an issue, especially if you want to do something other than just play it.