It very much depends on the background you have, actually. There's lots of ways to do it.
In Photoshop you have quick mask to paint the background away manually. There's lasso tool to trace the conture and magic wand to select colors. Photoshop has the Extract filter also where most of the job is performed by the program. And ther's a number of third party plug-ins like Mask Pro or Fluid Mask and the like. You'll find reviews of those here:
http://myphotosoft.com/select-tools/ Most of the plug-ins can be downloaded for a free trial period, by the way.