They are all open-source freeware programs.
TrueCrypt by TrueCrypt Foundation.
Summary: Creates an on-the-fly encrypted virtual partition out of a normal file, out of a normal partition, or out of an entire data storage. Encryption can be based on one or more key file(s), password, or both. Algorithms include AES, Blowfish, etc.. The virtual partition looks like a real partition to all non-system programs. Note: Once the virtual partition is mounted, it acts like a normal partition. Thus, a proper access control (i.e. chmod, NTFS, etc) on the virtual partition is suggested.
Platforms: Windows XP/2000/2003, Linux, and any platform if you can compile the source code.
Blowfish Advanced CS by Lasse Kolb.
Summary: Encrypt, Decrypt, Wipe file/free space (1x, 3x, 35x). Encryption can be based on key(s), password(s). The order that you enter multiple sets, if chosen, of them will matter! Encryption algorithms include AES, Blowfish, etc.. Compression algorithms include BZIP2 (recommended), Deflate, and LZSS. File names can be munged during encryption. After encrypting file/folder, the original is wiped. Note: You have to remember to re-encrypt your plain file after you are done working with it.
Platforms: All 32-bit Windows so far.