DEPRECATED: I recommend using 7-Zip's built-in hashing functionality that works in a similar way, integrating into Explorer.

HashProp - a better way to hash files in Windows

HashProp is a Windows shell extension that lets you easily calculate MD5, SHA-1, SHA-256, and SHA-512 hashes for any file in Windows:

For binary downloads, please visit the HashProp home page.

HashProp is released under the ISC License.