Secunia just came out with v. 2.0 of the Secunia Personal Software Inspector. In my opinion, this free application is an absolute must on any Windows computer.
Secunia PSI checks the programs on your computer for updates and informs you when they are needed. The new version will download and install most updates automatically. You can leave it in the default configuration, or configure it to discuss the issue with you before downloading. (Folks, like me, who are paranoid about installing Microsoft updates immediately on publication, may prefer that choice.)
If you’re not using Secunia PSI, you should be. If you have the older version, I recommend installing the new one.
You can download the application here, and they’ll walk you through the installation.
Note: Secunia PSI is on the verge of winning the Freeware Application of the Year award by a landslide. I just looked at the graphs.