Thinkwatt is a bash script for use with thinkpad laptops. However, as of v0.2, it works with all kinds of laptops as long as they've got a battery attached.

Thinkwatt can
 * record your power consumption,
 * calculate an average of that consumption
 * and visualize that data in a 2D gnuplot graphic.
 
usage:	thinkwatt -r (seconds) (-q) (-o file) (-f)
	thinkwatt [ -p | -a ] (-q) file

options:	
	-r, --record	record power consumption and optionally create a graph from the gathered data
	-p, --plot	create a plot image from one or two specified data files
	-a, --average	calculate the average power consumption from a specified data file
	-q, --quiet	makes thinkwatt less chatty
	-o, --output	the output file. can be prepended by a path.
	-f, --force	ignores the AC status. output may be useless, as power draw is zero until plugged out (avg is reduced as well)
	-h, --help	show this help text
	
examples:
	thinkwatt -r -f (will record to a temp file until cancelled, you may record the very events happening at AC removal)
	thinkwatt -r 300 -o /foo/bar/consumption.dat (will record for 5 minutes to the specified file)
	thinkwatt -p /foo/bar/consumption_bat0.dat /foo/bar/consumption_bat1.dat (will create a graph from the specified files)

Thinkwatt works with all laptops, not just Thinkpads.
If you're running thinkwatt on a Thinkpad it is still recommended to use tp_smapi as it provides more accurate results than the generic acpi.