Really convoluted and host service specific method to see and notify (beep sound) when players are online. See my email notifications bukkit plugin for something a bit more practical (at least for small servers).

(note: the download is here: http://www.mediafire.com/download/lxwkt27ccdykb1d/MCProhostingQuery1.3.6.jar) To launch/use, simply double click the jar. When prompted for Server ID simply go the control panel from your host for your specific server at the end of the URL should be the Server ID. The link url should be something like https://multicraft.mcprohosting.com/ and include the trailing slash.

chromestone - Main Project

ThePandemicMoon - Editor/Refiner