Comment on App Update

This is a widget, AppFresh is an application.
This gives you links to the pages where downloads are stored (checks VersionTracker, MacUpdate, and I belive for updates), AppFresh attempts to download them itself (and is a bit of a pain when it can't).

And, personally, I've had more luck with this than with AppFresh, though AppFresh is catching up. This also finds more updates, and gets less incorrect, last time I compared the two, so that's a definite plus (AppFresh fails completely on almost half of my apps).