www.malwarebytes.org Scan on demand (free) with real-time scanning just $25 one-time--not yearly! Malwarebytes' Anti-Malware software is one of the very best, and very light on system resources. You can load it up and run a scan periodically or when you feel you may have been exposed to a virus. Not only is scan-on-demand free, but the paid version is incredibly affordable, at only $25 on-time charge, for lifetime use!
First, grab Google Chrome if you haven't already http://chrome.google.com Then try the extension "adblock plus" to block annoying video ads on YouTube, Facebook ads, banners and much more. Enjoy surfing the web without obtrusive ads cluttering your screen. Try out other nifty extensions like facebook adblock, facebook fixer (to increase security on facebook).
Qustodio www.qustodio.com is free software that allows full control for parents, including individual child monitoring, time restrictions, content filtering, social network monitoring. OpenDNS www.opendns.com is not "software" but it is an excellent tool for blocking unwanted content at your router level, keeping all connected devices safe. (It requires intermediate level installation.)
McAfee's SiteAdvisor www.siteadvisor.com integrates with your browser, and most importantly will alert you to a site's potential threat before you go there, and show the result on any search in all of your favorite search engines. You'll get a lot less accidental viruses with this protecting you from malicious web sites! Similar software is available from BitDefender and Norton. Install more than one if you like!
Free graphics image editing www.gimp.org
Organize your images http://picasa.google.com
Real-time free anti-virus www.avast.com/free-antivirus-download
Audio Editing http://audacity.sourceforge.net