When I switched to MAC before half year now, the first application that I really – really loved was growl
Today I discovered another incredible tool, the GeekTool …!! 
GeekTool is an extra preference pane for your beloved Mac that allows you to display files, images and shell scripts on the Desktop.
Check the following sites how to setup GeekTool on your Mac :
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Ultimate GeekTool Setup – Pimp Your Desktop
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Monitor your Mac and more with GeekTool
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http://www.flickr.com/search/?q=geektool