Centralized update for third party apps

Solution 1:

I use AppFresh. It's nearly perfect. A lot of apps are recognized, even new ones and widgets and prefpanes too.

It's backed up by iusethis to check for update, but can also check for Apple or Microsoft Office updates.

Solution 2:

MacUpdate and Versiontracker both offer custom apps that do specifically this. However, after a free period, they're paid for I believe. MacUpdate app is my preferred of the two, available here.

Solution 3:

Bodega acts like the app sore in iTunes, but it's for desktop apps. It includes a version checker/updater in the "Applications" section.