In a recent hint it was mentioned that you could use your laptop as a lightbox for tracing artwork. Even better, you can trace on an iOS device, such as an iPad, with apps like Photoshop or Illustrator, if you want to trace something.
Using a screen forwarding utility like Air Display, you can use your iOS device as a secondary monitor for your desktop Mac. Simply drag your Illustrator/Photoshop/whatever window to that display, and you can walk around and trace whatever artwork you have displayed on the iOS screen. It servers as both the lightbox and the source artwork in one.
[kirkmc adds: I would be much more likely to do this with an iPad than a laptop, because of the iPad's glass screen. I guess you could even do this on an iPhone, if your art is very small.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20120217200309189