iStat Pro is a dashboard widget that allows you to monitor several aspects of your Mac computer. It's sort of like Activity Monitor, compressed into an easier to read interface that is accessible from the dashboard. With iStat Pro, you can monitor stuff like CPU usage, memory usage, hard drive space, computer temps, etc... Thank you, iSlayer.
Download iStat Pro

The OS X dock is one of the coolest features of Macs. It is also something that you are constantly using. Why not customize it? SuperDocker is a dock styler with plenty of options to choose from. They even have a community where SuperDocker users have uploaded their own creations that you can download. Thank you, SuperDocker.com.
Download SuperDocker

SuperDocker gives you an easy way to customize the dock. Candy Bar gives you an easy way to customize your icons. We actually have a tutorial on using Candy Bar, which you can read here.

OnyX is a multi functional application that allows you to configure hidden parameters and system settings within OS X. By using OnyX, you can easily adjust settings that you would normally have to use a terminal for.
Download OnyX

Sometimes there are some junk files left over after you delete a file from the trash bin. AppCleaner more thoroughly uninstalls programs and applications when you delete them. It has a very easy to use drag and drop interface.
Download AppCleaner

iAlertU is one of the coolest free mac softwares. By taking advantage of MacBook's built-in accelerometer, iAlertU allows you to set an alarm for your MacBook or MacBook Pro. Anytime your Apple notebook is moved or a key is pressed, an alarm will sound.You will need an Apple remote to use iAlertU.
Download iAlertU

Another of the coolest mac softwares. Caffeine is a simple application that allows you to disable display sleep and computer sleep with the click of the mouse. Great to use when downloading large files.
Download Caffeine

It's always a good idea to stay current with software updates and application updates. AppFresh simplifies the process by allowing you to manage all of your applications within a program.
Download AppFresh

An easy to use font manager application with advanced features. Allows you to preview all of your fonts within one window, easily import new fonts, etc...
Download Font Explorer X

Like the simplicity of OS X's built-in CD/DVD burning tool? You will love Burn. Burn keeps all the functionality of the standard burning tool, and stacks on several advanced features such as direct DVD burning.
Download Burn