Use Photoshop's Background Eraser Tool.

http://www.creativetechs.com/tips/quicktips_81-creative.html If you find yourself needing to quickly remove the background from an image in Photoshop, take a moment to play with the background eraser tool. The background eraser samples the color in the center of the brush. It deletes that color and softens the edges so that color halos are not visible if the foreground object is later pasted into another image.