Sophos Free Encryption does appear to offer good features for a 'free' product, with a trusted security company as the developer.

However:

* you need to register with Sophos to obtain it
* it's Windows-only
* expect the source code to be proprietary / closed, with all that entails on the encryption/security of the product
* availability of the program could be dropped by Sophos at any time.

7-Zip has the important advantages of being cross-platform between Windows and Linux (most desktop distros, as p7zip), is available from several sources, has useful file support, and is open source to review security effectiveness.

Another cross-platform alternative is zip files encrypted with GNUPG, although GNUPG is quite a heavyweight app on Windows compared to 7-Zip. (Don't use standard zip encryption (PKZip) though - that's really weak).