Reducing Arduino Power Consumption
Contributors:
Alex the Giant
Alex the Giant 
Resources and Going Further
More information on low-power modes and options can be found in the datasheet for the 328P.
For more power-related fun, check out the following SparkFun tutorials.
Adding a Timed Button to a Project
This tutorial will walk you through making a timed power controller for interactive projects. You will learn how to add an on button that will provide power to your project for an amount of time and then turn off again.
FemtoBuck Constant Current LED Driver Hookup Guide v13
The FemtoBuck board is a high-efficiency, single-channel constant-current LED driver.
Beefcake Relay Control Hookup Guide
This is a guide for assembling and basic use of the Beefcake Relay Control board
MicroMod Ethernet Function Board - W5500 Hookup Guide
Add Ethernet and PoE capabilities to your MicroMod project using the Ethernet Function Board - W5500.