Avast Antivirus has proven itself consistently effective over the years. Generally outperforming paid antivirus software, Avast's free Antivirus software is top-notch. I've trusted Avast for years, and it has served me well.

MalwareBytes is a very popular and very effective anti-malware option. Realtime protection is not available in the free version, but full system scanning and malware removal is. This is something I recommend the average user scans with periodically.

Comodo's firewall is among the best software firewalls available. The configuration may seem complex at a glance, but the firewall is easy to use after initial setup. Advanced users have plenty of options to suit their needs. I prefer Comodo's firewall to the one included in Windows. Note that you should disable the Windows firewall if you're going to use this.

CCleaner is a great way to remove tracking cookies, LSO cookies (the flash-based "zombie cookies" that have caused such an uproar among privacy advocates), temp files, history, and form data. As our personal data becomes less and less private, with web sites and companies of questionable integrity having access to it, I believe netizens should take measures to safeguard themselves against data mining and profiling. Using CCleaner regularly is one solid step in that process.