It's Here! Chris Odom's Physical Computing & Robotics with the Arduino IDE - Volume One

Optically Coupled Duel Relay Board

$4.00

These are the relay boards you are looking for. They take 5 volts to pull down the relay but trigger with just 3.3volts from the I/O, so they work great with newer ARM devices.

The relays themselves are rated at 10 amps. Unlike some other boards I have seen, these guys have pretty beefy traces as well....maybe not 10 amps....but certainly close.