Microsft Security Essentials - FREE anti-badguy software from Microsoft. Currently the top rated AV software solution available. Updates are silent, scanning is unobtrusive, and it doesn't 'sit' heavily on your while it's protecting you. Works great on systems without a lot of memory, and works even better if you've got more.

AVG Free - The next best choice in AV software and still FREE, although AVG has made the free version harder to find on their site, and once it's installed constantly asks you to upgrade to the paid version. The free version still works great, though I don't install it very often any more unless a client really wants it. The download link goes to CNet because it's easier to find than the AVG link (AVG wants you to get the paid version, probably.)

SUPER AntiSpyware - Another FREE AV program that's also a good choice, though not as fast or updated as often MSSE or AVG Free. SAS offers a portable edition that requires no local install and runs from a random .exe; useful for heavily inffected systems to restore stability but (IMHO) you still need to install one of the other programs afterward.

MalwareBytes AntiMalware - One of the best FREE program at getting out any deeply embedded nasties from a system. The free edition doesn't include any real-time scanning so it's something you either get into the habit of updating and using regularly or you'll use it to clean up after an infection. The D/L link goes to majorgeeks.com, the official download mirror. Don't worry, it's legit.

Carbonite - I know, it's not free. But for $60 a year, you get online automatic backups you can access from anywhere on any computer. I've set this up on many PCs here in Tehachapi and more than once it's been the difference between a disaster and a slight inconvenience. Easy, cheap, and reliable. You need this, get it.

Glary Utilities - Easy one button maintenance for your PC. Cleans up registry entries, old shortcuts, and (most importantly) gets rid all the temporary files in your system and empties your recycle bin. I use the Slim -No toolbar build at the bottom of the download page. The easiest to use of the so-called 'cruft' cleaners.

CCleaner - A bit harder to use than Glary, but only because it does a few more things. The Startup Tool is handy for finding out what runs when your PC starts up. CCleaner can also removed uninstalled programs from the Uninstall Programs menu, which is great when a program messily unintalls itself (I'm looking at you Norton...)