This week we’re going to examine the timely issue of data usage on your Mac. With the penalty for exceeding your quota as high as $150 per GB for some users, you need to know how much you’ve used and how much more you can squeeze out before midnight on your reset date. Here’s some options for users of the top 10 ISPs as rated in the 2008 Whirlpool Survey. (iPhone users: we haven’t forgotten you – look for a how-to on monitoring your iPhone data usage next week!)

Note: we’re looking here at methods to easily access the usage data provided by your ISP. It’s possible to measure the actual network traffic in and out of your router, but for 99 out of 100 users the ISP data will be sufficient.

Widgets

Menubar Apps

Firefox extensions

When it comes to Firefox extensions, there’s only one you need: NetUsage. Covering an astounding thirty-seven* ISPs this truly is the Swiss Army knife of ISP usage monitoring. Get it here.

iPhone apps

Here are three of the most popular and the ISPs they support. Note: links open in iTunes.

If you’ve got a favourite we haven’t covered here, post it in the comments.

* Yes, 37.