Open Whisper systems has partnered with WhatsApp to roll out end-to-end encrypted messaging!
I’m tempted to start using this once I hear more confirmation from security experts that it is actually fairly well done.
If you aren’t familiar with encryption, this means that your device encrypts the message before passing it to the receiver. Since this is done at the device level, WhatsApp is unable to decrypt your messages even if they wanted to. This completely foils the NSA’s automated data gathering and many kinds of search warrants. It still allows the government to require that WhatsApp introduce a backdoor, but hopefully they have a canary for that.