We built Naptime - the nicest word we could think of with the letters NPM contained in order - to show the dependencies of a node app and if they are out of date.
You can enter a package.json file (either paste in the textarea, or drag and drop on the page). The release history will show in a series of charts and you can see where you stand on it.
We got the data straight from registry.npmjs.org, used a bit of express, knockout & bootstrap. We also used some version matching from npm (but ran it in the browser - hooray for javascript!).