Youtube video showing a relay switched by a transistor, controlled by an Arduino:
Here is a PDF of the circuit diagram:
Here is a page describing setting up a relay:
After playing around with the arduino controlling the relay, it became apparent that there was some voltage buildup. I first thought it might be a need for a snubber diode. I replaced the non-polarized non-DIP relays with polarized dip relays. To each relay I added a snubber diode: a 1N4004 Diode. The Integrated Circuit doesn't handle driving relay voltage well, so when the relay powers off, there is usually a voltage spike that makes the I.C. do a little hot foot dance. In order to get around this voltage spike, I added snubber diodes and used polarized coil relays. However, it seemed to still be an issue, so I decided to additionally isolate each relay cricuit with a transistor (as shown in the examples above). I went with a trusty 2N2222 transistor.
You can see the 5V Voltage Regulator on the bottom left of the above photo. The voltage regulator takes 12vdc and converts it to 5vdc. It also gets hot. I setup the relays to use the 5vdc, and will also pipe it to the servos, eventually.
Here is a tutorial on the 5vdc voltage regulator and an arduino:
The underside of the mostly finished relay board.