It depends what you want to do. If you are placing the cut out pieces into a catalog, you would probably be advised to learn about clipping paths. Photoshop Help should give you the details (sorry, I'm a bit stuck for time today, so I can only point you in the right direction!)
If you are adding the background in Photoshop, then there are a number of options. You could try the Filter > Extract... tool. If you go this route, you would be better off using a completely different color background (black might end up blending into the shadows making it harder to distinguish some edges). A bright blue or green could work -- it's good enough for Hollywood!
Also, if you use, say, a bright green, you will have an almost ready made mask in the form of the green channel. Duplicate this channel, use Levels or Curves to make it into a sillouette of your product, then you can use this to mask out the object.
Again, apologies for being economical with the details, but Photoshop Help can fill in the gaps!
