This is by no definition of the term complete. Please help by correcting my mistakes or points I may have missed. Use it as you see fit but what you do with it is not my responsibility. If this isn't allowed, please remove it.
GPG
Links:
http://www.gnupg.org/ - Main GPG website
http://www.gpg4win.org/ - GPG for Windows
What is GPG:
In simpler words: GPG is a tool used to sign (to prove authorship) and also to encrypt messages or files to ensure only the intended recipient can access the decrypted content. Pictorials:
Windows - Installing GPG4Win
Windows - Creating your first public key
Windows - Exporting your public key
Windows - Basic text encryption
Windows - Basic text decryption
The commands in those pictorials should work with both Mac and Linux aswell. The installation, however, would be different. TODO:
Signing
More detail
GUI version (Using Kleopatra)
Flesh this out
Add some basic truecrypt information?
Fix errors?