Is there a wall outlet power meter that I can interface with from a computer?
If you're willing to do a little modification, you can use a Kill-A-Watt and hook it up to your computer.

Adafruit has a "Tweet-a-Watt" project that interfaces with a Kill-A-Watt and wirelessly sends the power readings to the receiving unit (which they then hooked up to tweet the current readings)



In the Adafruit forums, I found a guy who was trying to read the Kill-A-Watt directly with an Arduino, instead of wirelessly sending the readings. You could use an Arduino and read the measurements directly into a serial console on your computer and save the results to a file that way.