HashCheck is an Explorer extension which makes it easy to create and verify file hashes, handy for spotting when files have changed.
Creating the hashes is as simple as selecting a group of files in an Explorer window, right-clicking and choosing "Create checksum file". By default this creates a "checksums.md5" file in the same folder, although you can specify another name if you prefer.
Next: wait. Or install an application, remove another, do something which might change one of your checksummed files.
Finally, double-click the MD5 file to open it in HashCheck. It displays everything it hashed last time, and highlights any files that have changed or are missing (they're tagged "unreadable").
HashCheck can also verify SFV and similar checksum files created by other applications.
HashCheck hasn't changed since 2009 and has no frills at all, but it still handles your basic hash-and-verify tasks with ease. Not bad for a download size of only 85KB.