As far as software goes, a combination of dd / ddrescue / strings / fdisk / grep / mount / and the r-studio suite from r-tt.com are what I use. Though, most of the time the drive is physically damaged, and it's not always inside.

For example, last week I had a laptop come in with no power to the drive. I examined the board with my eyes and my Fluke Multimeter and discovered that the power +5V on pins 41 and 42 wasn't reaching very far into the board and was basically disconnected at the first component. It looked to be a power-protection diode which had blown due to a surge. I was able to bypass it with a dot of solder, and once reassembled the hard drive powered on, I copied the data off. When the customer decided he didn't want to pay, well, I removed that solder dot before returning his drive to him without his data...

On 3.5" hard drives you'll often see a rectifier diode serving the same purpose, so when you run into a drive that doesn't spin up, check that out first. It's a small black component connecting the power to ground, and it shouldn't be passing electricity (but it will when it fails, so just pop it off to get your drive working again).

Other times a clicking drive can be fixed by just swapping out the board with an identical one from another drive. Sometimes, similar model number boards will work as well, but not often. It's a lot of fun trial and error. On the plus side, if the drive is totally fubar'd but still spins up, you can pop it open and do some hard drive spin art!