For power users and other keyboard-shortcut fanatics, Keyboard Maestro is one of those apps that--once you've used it for a couple weeks--you wonder how you ever lived without it. (And, in fact, Keyboard Maestro mimics the functionality of many other much-beloved productivity-enhancing apps, even including the Classic Finder.) Keyboard Maestro's Program Switcher and Window Switcher make cycling through and managing open applications and windows a breeze, and its Clipboard Switcher lets you work with and store an endless number of clipboards. Keyboard Maestro also supports Growl and AppleScript, with the option of automatically pasting in script results at a current selection.
Where Keyboard Maestro really shines is with its powerful and easy-to-use macro capabilities, with a built-in Web server that even lets you run macros remotely from a browser or from the Keyboard Maestro Control app for your iPhone or iPod Touch--and you can take a wide variety of remote actions, from shutting down your Mac to running an Automator workflow to controlling QuickTime Player. You can also execute macros using hot keys and "device triggers," such as mouse buttons and programmable keyboards. The possibilities with an app like this can be a little overwhelming, but thankfully Keyboard Maestro comes with excellent documentation, including a Quick Start guide and copious macro examples.