I don't know how complicated you want to get with it, but there's a tool in PS called the Pen tool that you can trace the outside of an image/shape with it, save the path it makes, and select that to get just that part of the image. This does away with nasty pixel jangley bits at the edge of whatever you're cutting or deleting.
(I have to use the bloody thing all the time at work so I'm used to it, but it takes some practice)
I Googled "Photoshop Pen Tool" and found this that looks like a decent tutorial on how to use the pen tool if you're interested.
http://www.melissaclifton.com/tutorial-pentool.html