Magnetic Lasso tool Enables you to draw around stuff fairly accurately. Takes a bit of tweaking sometimes but it;s pretty good.
Also, I tend to use another option called the Quick Mask tool. It enables you to paint onto the photo/picture which then turns into a selection at the click of a button. Hard to explain, but it's something like a masking/overlay tool.
If you can get it, or know a mate who has it, Photoshop Elements (about Â£50) has an extract tool that is powered by witchcraft - it is unbelievable, and about 100 times easier than doing the same thing in Photoshop. I think they may have incorporated it into Photoshop CS4, but I don't have that so can't confirm.
It's definitely in Photoshop Elements 5 or above.
If you get the chance to give it a go or see it in action try it - you'll be amazed. There might be a demo on Adobe's website.