monline

I already posted about HashTab, a utility available for both Windows and Mac OS X. It integrates well with the OS and allows you to generate MD5 (or other) checksums easily. There're a couple of alternatives in case of Windows though.

A quite popular one is digestIT 2004.
It's notable features are:

• Integrates itself into Windows Explorer (simple right-click interface)
• Multiple file support
• Save result to file or copy to clipboard
• Native support for 64-bit Windows (x64 Editions)

However it has a small bug with files larger than 2GB: The only issue of which users need to be aware is what is called the "2GB limitation". What this means is that the progress indicator will not properly display the file size and processing progress of files that are 2GB or larger in size. However, the final result displayed for such a file will still be correct.

Another alternative is MD5sums. It does not integrate with Windows out-of-the-box, but a simple right-click (Send To) integration can be easily added by the user.

Microsoft released a checksum tool too, but they didn't go too far with it featurewise. It's a commandline only tool and MS does not support it in any way. The name is Microsoft File Checksum Integrity Verifier.

And in case you're a GNU fan , the Windows port of the GNU coreutils package contains a free, GPL implementation of the md5sum command.