I just stumbled upon OpenStego and found it to be an interesting program.
Program: OpenStego
License: Open Source/GPL v2.0
Description: Steganography is the science of hiding secret message inside another larger and harmless looking message. This is one notch above regular cryptography; which just obscures the original message. Steganography tries to conceal the fact that there is a message in the first place. Steganographic message often appears to be something else than the original (secret) message, like a picture, sound, larger text, etc.
Website: http://openstego.sourceforge.net/
Just a bump to add my vote for this program being added to PortableApps