- Truecrypt for encrypting sensitive files, folders, and entire drives on your PC.
- GPG, an open-source implementation of the OpenPGP protocol used to encrypt email communications. Be sure to read up on why standard-compliant email messages can never truly be secure, though.
- TAILS, a.k.a. The (Amnesic) Incognito Live System, a Linux distribution built with security and anonymity in mind. TAILS comes packed with numerous privacy and encryption tools baked in, including Tor, which allows you to browse the Web (mostly) anonymously and access a Darknet of so-called "Hidden Services" that grant anonymity to both web servers and web browsers. Bruce Schneier--a longtime security guru who has actually read the documents detailing the NSA's encryption-busting methods--recommends using Tor and Hidden Services to thwart NSA surveillance. TAILS is meant to be used as a live CD, which means you can boot it from a disc or USB drive, and your data is wiped when you power off your system.
- Off-the-record messaging, or OTR, a cryptographic protocol for encrypting and authenticating instant-messaging communications. The protocol uses AES and SHA-1 standards and comes baked into TAILS and is recommended by Schneier even in the wake of the NSA revelations. Here's a list of IM software that supports OTR.
Proprietary encryption tools created overseas may -- may -- also be less likely to have installed NSA-friendly backdoors into their software. This morning, I received an email from Boxcryptor, the superb (and Germany-based) cloud-storage encryption tool, reassuring me that there is no way for the company to snoop on its customers, as it encrypts files using private RSA security keys storedonly on users' private PCs, then transmits the already-encrypted files using HTTPs.
Beyond encryption, most of the advice in PCWorld's How to protect your PC from Prism surveillance still applies. Note, however, that the New York Times report on the NSA's crypto-cracking abilities suggest that VPN technology and the ever-popular SSL web protocol have been two encryption methods particularly targeted by the government. (Schneier suggests using TLS and IPsec whenever possible on the web-communication front.)
Even so, using the tips in that article will make your browsing much more secure in general, not just the NSA or foreign governments.
Also check out PCWorld's guide to encrypting (almost) everything, which is chock full of handy-dandy encryption tips, though many rely on proprietary -- not open-source -- technology. While closed-source solutions may not protect against The Man and his super-encryption-cracking eyes, they'll help keep everyone else out of your business.