I like free software that are:
1) Free without any strings attached
2) does not require install so you can be sure you're not installing spyware
3) Is lite and portable so you can run it off of a USB memory stick
4) is open sourced so it has been inspected by others to be free of malware
With that said, here are the software that I cannot live without:
is a powerful encryption software that you can use to safely store your personal data. I have made believers in TC out of all my family, friends, and co-workers.
is a lite and ultra robust password manager with a highly secure encrypted database. It is very rich in functionality and yet requires no install and runs on all Windows platforms.
is a very cool, lite, and easy to use TO DO list manager with a lot of cool features. Again it requires no install so you can download and try it out without any risk.
4) Darik's Nuke & Boot Disc
is a utility that securely wipes out data on a hard drive. Use this utility with care!! Once you use it your data is lost.
All of these software require no install so you can try it out without risking changing your OS state.