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.