Mac: iStat pro Dashboard Widget
One of the first applications I downloaded and installed on my Mac was iStat menus, a wonderful little add in to the menu bar. iSlayer also produces a little dashboard widget called iStat pro.
If you like to use your dashboard and want a quick summary of the health of your Mac you should check it out. Takes seconds to download and install. It has the one thing I wish iStat menu would have: a battery health monitor.
You can download it from the Apple Downloads area.
There actually is a way to check the battery health using iStat. In the options for the widget you can include or exclude various things that can be monitored.
I believe it shows the amount of cycles, the overall status of the battery's health, and the current charge level.
It measures cycles as the amount of times the battery has been fully charged.
For example, charging from 60% one day, and then charging from 40% to full the next, is considered one cycle.