As the Leopard application upgrades roll in I've been increasingly using a great little application to keep all of my applications up to date. It is called AppFresh and you can download it right here.
AppFresh helps you to keep all applications (third-party and Apple), widgets, preference panes and application plugins on your Mac up to date, from one place. It works by checking the excellent iusethis.com database for new versions and lets you download and install available updates easily. Check it out.