There isn't an engineer out there who hasn't, at one point, wanted a robotic arm. Unfortunately, they're quite costly. Dan Royer from Marginally Clever, however, has released an open-source 3DOF robotic arm that is sure to get many excited.
While the robot in the video is only his first prototype, you can easily see that it is quite capable. Dan built-in one nice approach -- an understanding of inverse kinematics. This means that instead of having to program specific transitions and positions for each motor or servo in the chain, you can simply give the robot coordinates where you want the tip to be and it will figure the rest out. This saves so much time and reduces trial and error considerably.
You can download the code as well as the design files for the arm on his page. Keep an eye on his site, because his ultimate goal is to build a low-cost 6DOF version. He isn't stopping development on this version either. Immediate plans include bearings for smoother movement and a nice openGL based interface to allow for you to manipulate the arm visually.