You can encrypt just a few files or your entire hard drive with the open source TruCrypt. In the file mode, TruCrypt works by creating a single file that, when unlocked with your pass phrase, mounts itself as a drive on your system. Anything going into this drive is then automatically encrypted. You can then dismount the drive at any time. You can also use it on a flash drive with their own built in utility so you can keep an encrypted file on the flash drive and open it with any computer. I use this in combination with Portable Firefox on a flash drive that I keep on my work computer. I then use it when I’m traveling and need to visit a secure site, such as my bank or credit card. This keeps all of my passwords, account info and all of that sensitive data encrypted and off of my work computer while still leaving me very safe access to it.