Encrypt your files with AES to a virtual drive or Cloud, using Cloudfogger
Cloudfogger is a free program that will help you encrypt your files easily, using AES (Advanced Encryption Standard, approved by the NSA for top secret information). Client-side encryption ensures that nobody will be able to access your files without your password.
Cloudfogger uses transparent encryption, you can use it to save your files to a new virtual drive X that is created when you install Cloudfogger. In the background, all files stored on X will be written fully encrypted to a selectable directory on your system, for example your Dropbox. This works also with cloud storage providers or even local network/disk storage.
Cloudfogger-protected files can also be shared with others. You just need the automatically created Cloudfogger ID your partner uses.
The portable Cloudfogger file format makes distributing files via e-mail or USB sticks easy.