I've been mucking aroound with a project that uses off the shelf servos... it's kind of like the awesome BRAT here http://www.lynxmotion.com/Category.aspx?CategoryID=97.
At the moment I'm breaking out the digital ports to a breadboard, which I have pins that servos can be plugged into. For the next stage of the project I wanted to make a shield which would have the pin configurations needed.
I started mocking this up in eagle, but I quickly realised that I was under-utilising most of the functions of the Arduino board, and that with a few dicrete components and a AtMega8 I could make a smaller standalone board.
I've made it up in Eagle, modifying the USB-arduino schematics. AS it's designed for running servos, I call it the 'Servuino'. It has 6 servo ports, 5 digital input ports, and has the TX/RX ports for serial communication. It takes any power source greater than about 5.7V.
At the moments it's single sided so I can make it easily at home, and it comes out at about 35mm by 60mm, or about 2/3rds of the height and width of the USB arduino board alone. Ofcourse it has correspondingly less functionality, but if you include a seperate board for servo pins it's a good space saving.
Although my design only needs 6 servo and 5 inputs, I'm sure someone could come up with a better design to somehow fit in the analog and remaining digital ports. Also I'd love it if anyone could check it over for any errors, it's my first time making a PCB design. Any comments very much welcome.
Here's the schematic: http://files-upload.com/files/7039/Servuino.sch.html
And the board: http://files-upload.com/files/7041/Servuino.brd.html
(scroll down and wait for the counter to reach zero - let me know if there are better forum file-hosting sites out there)