Paste without formatting

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Open 'System Preferences'
Select 'Keyboard'

Select tab 'Keyboard Shortcuts'

Select 'Application Shortcuts' from the left listbox
Click '+' below right listbox

Select 'All Applications' for 'Application' input box
Type 'Paste and Match Style' into the 'Menu Title' input box
In the 'Keyboard Shortcut' input box, pretend that you are about to paste something by typing command-v. There should now be the cloverleaf command sign followed by a -v in this box.
Click add.

source: http://ask.metafilter.com/187733/OSX-How-to-copy-plaintext-always-everywhere-without-exception