Heard about a fantastic little (under 800KB installed) Freeware utility called PSI on a security Podcast this week.
What PSI does is to trawl your system for programs in it's (extensive) database that are known to have security issues.
If it finds an offending program that it knows has been patched to fix the problem, it will alert you to this, and, give the link (URL) to where the latest download can be obtained.
Let's make it clear that it is NOT designed to alert you to the latest versions of all your software, just the ones that it knows has/hade security issues, and it's not a virus checker...and it's FREE!!!
Download PSI here:http://secunia.com/
(They have other stuff that I've not tried yet).
One caveat: PSI has to 'phone home' when you run it (to download/update it's database), but this takes no time at all (they use an open source compression algorithm)...just be aware that you need an Internet connection.
Used it on a virtually brand new Laptop (Vista Home Basic), and it warned me that the Flash software was vulnerable and gave the link to the latest version!!!
As Freeware, this is an amazing piece of software that you really should try.