Below is a list of the more 'well known' free encryption software.

Freeware To Help Keep Your Personal Data From Prying Eyes

PGP Freeware
It is a tradition at PGP to offer a limited capability version of PGP Mail for individual, non-commercial use. PGP Freeware offers basic PGP encryption capability for messages and files, but does not include many features available in other PGP products. There are versions available for both Windows and Mac environments

Truecrypt
Certainly one of the top file, folder, disk or key encryption programs.Free open-source disk encryption software for Windows Vista/XP, Mac OS X, and Linux Main Features:Creates a virtual encrypted disk within a file and mounts it as a real disk.
Encrypts an entire partition or storage device such as USB flash drive or hard drive.
Encrypts a partition or drive where Windows is installed (pre-boot authentication).
Encryption is automatic, real-time (on-the-fly) and transparent.
Provides plausible deniability, in case an adversary forces you to reveal the password:
Hidden volume (steganography) and hidden operating system.
Encryption algorithms: AES-256, Serpent, and Twofish. Mode of operation: XTS.

Buddy
Be safe, the encryption used by File Buddy has no known successful attacks against it - so you can feel at ease knowing your data is truly protected.

CryptMage
CryptMage is a file encryption tool using a proprietary algorithm to secure your files and data. Easy to use.

Iron Key
Iron Key is a program for encrypting files that you can safely send over the Internet. The encrypt file is a self-extracting executable - your correspondent must run it and enter the right password for decrypting. No crypto software needs to be installed on the receiving side!

Ddcrypt
encryption utility that supports encrypting directories as well as multiple files, shell extension included, updates are coming soon.

EyeMage IIE
Eyemage IIE allows you to encrypt any file or text into a bitmap image. You can hide photos in photos, zip files in images and word documents in diagrams.

HandyBits EasyCrypto Deluxe
Try this state-of-the-art encryption utility. This is really the easiest and most reliable way to secure your data with strong encryption.

Kryptel Lite
Kryptel Lite is a free version of Kryptel. While it lacks some advanced Kryptel features, it is a fast and easy-to-use program, which will perfectly suit your needs if your security demands are not very high.

GRL RealHidden
GRL RealHidden version 1.0 is a software utility that allows you to hide a file physically inside of another file, and then retrieve that hidden file.

Hide In Picture (HIP)
Hide In Picture (HIP) is a steganography program. It is a program that allows you to "hide" any kind of file inside standard bitmap pictures. The pictures look like normal images, so people will not suspect they contain hidden data

SiFEU
SiFEU is a program that in an easy way lets you encrypt files with very strong encryption. SiFEU uses the Blowfish algorithm for file encryption, SHA1 for calculating the hash sum of the password and the Gutman pass-35 pattern for shredding the source files.

PowerCrypt 2000
OVSoft PowerCrypt 2000 is the innovative and powerful file encoder. Make sure your files safe with a 100% secure encryption algorithm.