Due to recent developments in software and hardware, some consumer-level encryption products are now so powerful that law enforcement officials say they can't crack them, even with massive supercomputers. (Washington Post)

If you just want to deter prying eyes a substitution cipher using multiple substitutions and several different substitutions schemes offers a reasonable level of encryption for virtually no computational effort. (TechWorld)

There are free on-the-fly disk encryption / on the fly file encryption (OTFE) software that transparently encrypts files on your disk drive (or partition), on demand encryption tools that allow you to encrypt single files for those one-off occasions when you need encryption public key encryption which is particularly useful for things like email (where the key you use to encrypt your data is different from the key used to decrypt the data), etc. (thefreecountry.com)