Autograph by Ten One Design, does what should have been possible years ago, namely sign your name digitally using your laptop's trackpad. The app resides in the menu bar, can be invoked by a hotkey, and you must sign with your finger – not a stylus. At this stage, it's also limited only to unibody MacBooks using the latest MacOS X version, Snow Leopard. On the plus side, it costs only $7 (free if you buy the company's Pogo Sketch app) and there's a free/trial version with no time limit that adds a watermark to the signature.
(Source: Macworld) | Cost: US$7 | Requires: Unibody MacBook & Mac OS X Snow Leopard | For further info