Are My Sites Up?, the uptime monitoring service, now has an application for iPhone users that lets them keep an eye on all their domains when they’re away from their computer.

While the service offers free SMS and e-mail notifications in the event that your site goes MIA, there hasn’t been an easy way to add new sites on the go, which this app does in spades.

You can add and edit new sites to keep an eye on, as well as delete them entirely. There is, however, no way to set what kind of notifications you want to get for each domain, which I’m told is coming in a future revision. Another small caveat is that you must subscribe to one of the service’s three premium plans to use it, so free users cannot partake with this version, which does cut down on its usefulness.

While this app isn’t much to look at just yet, it’s one that could be promising with the upcoming iPhone OS 3.0 update, which enables push notification in third-party apps. This means you could get real-time notifications when one of your sites is down even when the app isn’t running. It would also let you hop straight to the site to double check.