Attach a sketchpad device to a MacBookPro to make use of sketch-enabled apps
Yes, you are right.  Here is one manufacturer of those kinds devices:

Wacom

I would recommend the Bamboo Tablet, it is a cheap and effective solution for what you are asking, they connect through USB and are very easy to set up and calibrate:

Bambo Tablet

They also make more expensive input tablets but I would only recommend that if your are doing very professional editing/art creation because they would be over kill for many people who just want to simply draw and sketch ideas and make art. 

Most/All of the these tablet/sketch input devices work as alternative mouse inputs, so you can use this with your mouse or as a replacement for it.  They are even pressure sensitive allowing for multiple degrees of precision and line thickness.  They also usually come with basic art software like Photoshop Elements or Basic painting/drawing software like Autodesk SketchBook Express.  For only 50 to 79 dollars for the basic tablets, you can't really go wrong.

I hope that this information helps you out.