LightDisk is a little application that sits on your system bar, near the clock.
With this application you can forget about check your disk space, it will check automatically for you and advice if you're filling it. Also it can send an email to your account if needed.
Just keep your disk light.
Recommended for your forgetfully friends!
* compatible with HFS, HFS+, Fat and exFat, only if the disk has write permission for the current user