For a decent overview of 5 different techniques for isolating a foreground object, have a look at the following link.
http://www.sitepoint.com/print/masking-techniques-photoshop
From the article:
In this article, we'll explore five different methods to isolate objects in Photoshop. As you follow this tutorial, you'll gain a how-to explanation for each technique. You'll also get the stats on how long each method takes, and my opinions as to when each method is most appropriate.
The methods I'll demonstrate include:
* Using Photoshop's Magic Eraser tool
* Using Photoshop's Background Eraser tool
* Using the Extract command
* Using Quick Mask mode to make a selection and layer mask
* Using the Pen Tool to make a selection and layer mask
