I'll start this list of tools with a small and very useful tool to clean up useless files from your Windows PC.
It is a free utility, 3Mb in size, and with it you can clean unnecessary files from your Windows computer. It also features a Registry cleaning tool. You can also integrate it with your Recycle Bin for easy access.
This utility comes from the same developer and is a simple defragment tool for your Windows computer. It is fast and better than the one that comes with Windoze.
SpyBot S&D (free)
Finally a free Anti-spam utility to shield you from malicious websites. It protects your pc from malware with a huge list of blocked addresses that this program injects into your Windows Hosts file.
I use these three utilities almost daily, except defraggler which I use once per week. SpyBot SD issues updates regularly and with it you can surf the web with a clear mind.
Ofcourse you should accompany SpyBot with a real-time antivirus and a firewall to ensure maximum protection against attacks and viruses.
If you have a suggestion for this list please leave a comment and I'll include it with the rest!