Microsoft just launched the download for their free Microsoft Security Essentials we reported about earlier today.
Microsoft Security Essentials provides real-time protection for your home PC that guards against viruses, spyware, and other malicious software.

The new free security software, independently certified by West Coast Labs, is backed by the company’s global security response team and is built on the same award-winning core security technology found in the company’s security solutions for businesses.
Microsoft Security Essentials runs quietly and efficiently in the background so that you are free to use your Windows-based PC the way you want—without interruptions or long computer wait times.

As said earlier, it needs to be seen if Microsoft Security Essentials is the only security software that you need going forward, or if you still need to buy software from Symantec and McAfee on top.
More details on the Microsoft Security Essentials site.