The Usage Agent toolset is designed to help manage your ISP data usage without having to log into your ISP usage page. It can optionally monitor your network card throughput and produce reports on usage.
It's released under the GNU General Public License. Take a look and see if it suits your needs.

Usage Agent now works for the following ISP's:

Optus, Telstra/Bigpond, aaNet, Exetel, Exetel Wireless, AAPT, OntheNet, g-node, amnet, dodo, EFtel, Internode, ComCen, Westnet, Spin, BettaMomentum, Adam, Netspace, TPG, Blitz, Soul, Webshield.

UA Wallpaper showing web form and ISP Usage

Icon text Statistics