Personal Software Inspector
You probably have 20-30 different programs installed on your PC. Do you know if all of them are up to date? Are you running the latest version of Java or Flash? This free tool gives you an automated way to scan and report for over 7000 applications.
A security company called Secunia has a great little utility called Personal Software Inspector. It is a free tool with the sole purpose of helping you secure your computer from software vulnerabilities. It can be found here.
They maintain a db of all the known vulnerabilities for thousands of applications and compare what is installed on your PC to that list. If it detects an installed program that is either out of date, end of life, or vulnerable it will alert you. Not only does it alert you but it also directs you to information on how to update it and what the exploits are about.
With this tool you never have to wonder if you have everything updated. You no longer have to scour the message boards looking for new exploits that might make you vulnerable. It does it all for you. Did I mention it is FREE?