Below are links which you may find useful: We use these here on our PCs and can recommend them

Essentials
Spybot Search & Destroy	Excellent free software for searching for and removing Spyware infections on your PC. There are a lot of fake sites about that sound similar so make sure you download this from the correct site to avoid even more problems.
Malware Bytes Anti Malware	As above. Highly recommended.
CCleaner	Free software that can clear out all the temporary files that will start to clog up your PC, it's configurable so that you can choose what to remove.
AVG Anti Virus 8.5 Free	Free for home and non commercial use. This Anti-Virus software is our choice of protection on the home PCs here.  AVG also offer full internet security products for home users and businesses (and they don't consume PC resources like some sym.. Mc.. products do) . We are resellers of AVG so contact us for more information. We now recommend AVG Internet Security for all home computers which is available from us at a discount on the retail price on the AVG site.
Good Stuff
Cooliris	Adds a 3D look to sites that support it. Works great with a Google image search.
Worldwide Telescope	If you are into the stars but have never got around to getting a telescope this is a great site to visit. The about page is here, below is short extract: "The WorldWide Telescope (WWT) is a Web 2.0 visualization software environment that enables your computer to function as a virtual telescope—bringing together imagery from the best ground and space-based telescopes in the world for a seamless exploration of the universe. "