I wrote a bandwidth-usage Dashboard Widget for Adam Internet a while ago. They have since changed their quota system to use "onpeak" and "offpeak" quotas, breaking my old Widget. I've now updated it for the new system.. I may create a nicer widget at some point, the current code is a bit of a mess, and I have an idea for presenting the on/offpeak data better...)
Admittedly there's probably around zero other Adam Internet customers reading this, but it should appear in search engines, should someone be looking for such a widget..
Anyway, how it looks:
You have to set your Adam Internet username and password by clicking the
i at the bottom left (it appears when you hover the mouse over it)
The only possibly non-obvious thing might be the green light - this indicates if it is currently onpeak (8am till midnight), or offpeak (midnight till 8am)
..and the download link: