Real life story: A consulting client of mine called in a panic: her Macintosh wouldn't start up. This is every designer's nightmare! It was an older Mac, she was planning on upgrading soon anyway, so this accelerated her purchase of a new Mac. But she had lots of valuable data on her old Mac.
Based on her description of the non-responsive Mac, I suspected the hard drive was OK. When her new Mac arrived, I pulled the hard drive out of the old Mac, and used the $29.99 USB 2.0 Universal Drive Adapter from Other World Computing to temporarily connect the old drive to the new Mac. It worked flawlessly. I was thrilled by how quick and simple it was, and she was thrilled to have her data back.
Yes, there are other ways to do this, but the Universal Drive Adapter is inexpensive, quick and easy. It allows almost any 2.5", 3.5" or 5.25" hard drive or optical drive to be temporarily connected via USB to a Mac or Windows computer. Highly recommended if you need this sort of thing.