Malwarebytes' Anti-Malware is a free program that runs along side your antivirus program. It is not a replacement, but a "sidekick". That doesn't mean it is any less useful. It is very useful! And in many occasions it has caught infections that slipped through the antivirus software.
Microsoft Security Essentials (MSE) is an excellent, free antivirus program from Microsoft. This means no Windows user has the excuse to not have an antivirus program. A FREE antivirus program.
File Reassurance — aka Backup
SugarSync is an online backup and syncronization program that saves your files securely in the Cloud. It starts out at 5GB for free and from there you can gain more space with referrals, where each party receives 500MB bonus. There are also many paid subscription plans. I feel that overall, it is the best option available. There are lots of other options such as Dropbox and Windows Live Mesh (which I both use along side of SugarSync for even more space online). However, if I wasn't a broke college student, I think I would pay for SugarSync so that all my files are in one place.