What it is: A menu extra that provides at-a-glance statistics relating to CPU usage, memory, drives, your network, drive temperatures, fans, Bluetooth and date & time. Stats are shown in the menu bar, and each item’s menu provides further information.
Why it’s good: It’s fast and it’s stable, plus, unlike many similar applications on the Mac, it’s free. Set-up is absurdly simple, done via a System Preferences pane (although, iStat menu guys, being able to open configs directly from each menu would be a nice idea). The crowning glory is the Date & Time module. It enables you to show the time and date simultaneously in the menu bar, and the item’s menu provides a simple calendar and optional world clock. All three of these things are available as individual shareware via other companies, but here they’re all integrated, well implemented and free.
Where to get it: iStat menus is available from the iSlayer website, and even if you only use the Date & Time module it’s worth a look. Note that if you use the app very regularly, a small donation will help iSlayer work on future verisons.