Going over your allocated bandwidth isn’t the best of surprises.
Orcon Widget for OS X – Download
I made this simple Widget a few years ago to keep track of my internet usage. Coding this up for my current internet provider, Orcon was a simple matter as their usage display mechanism on their website works by identifying your usage by the static IP you have.
The widget displays your total usage (uploads and downloads) and updates as frequently as Orcon updates their usage tally (in other words, it is not real-time).
Edit: Sorry, uploaded the wrong file before. Problem fixed.