Launch! Netspace is a Mac OS X application for Netspace ADSL broadband users ( http://www.netspace.com.au ). Launch! Netspace provides a usage meter that updates automatically while connected to the network, calculations of costs when over your monthly allowance, and a status menu item.
Launch! Netspace is donation-ware - which pretty much means it is freeware (no nag screens or limitations) but I appreciate donations if you find the software useful. See the Web site for details.