Antivirus

Panda - link to website
Scan your system for viruses online. Free. No software to install

AVG - link to website
Full, free antivirus software download

Firewalls

ZoneAlarm - link to website
Probably the best known free firewall - make sure you choose the link for the free product

Malware Destruction

Spybot Search and destroy - link to website.
Free application to scan for spyware, adware, hijackers and other malicious software.

Ad-Aware Personal - link to website
Free version to scan for spyware adware etc

Web Browsers

Mozilla Firefox - link to website.
Free, fast and efficient. Basic version is simple and easy to use. Lots of add-ons available from their site to make the application feature rich.

Opera- link to website.
Free version has adverts. If you buy the product the ads are removed. Fast and efficient. Feature rich interface which some may find overwhelming.

Office software

OpenOffice - link to website.
Free. Claims to be able to duplicate nearly all features found in Microsoft Office.

Data encrytption software

Iron Key - link to website
Encrypts single files - free version is called iron key - other paid versions with advanced functions (e.g Silver key) are available