CrossOver is a sick app that allows you to run Windows Apps on your Mac without booting a different OS.
iStat Pro 2 is a nice and handy widget that shows your Mac's Stat's (Ex. Temp. CPU Usuage, etc.)
UnRarX is a .rar extractor for Mac.
DiscAid or PhoneView are Direct SSH(view/edit/add/remove files on your iDevice) programs if you have an iDevice.
ScreenView is a Simple Screen Recorder
aMSN is MSN for MAC
AppCleaner is a Must-Have app for your mac because it's the fastest and most effective way of removing an App.
Those are some of my apps I have on my Mac.

:bro:
Edit:
Some links to some "Must-have" apps for Mac.
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