Here is one more site:
http://geomag.usgs.gov/models/models/
Click "Start GeoMag" to start their online calculator.
Click "Load model" and select "igrf-2005" for the current "epoch",
then Type In your Latitude / Longitude (with "-" for US).
Then click "Calculate". Look at the line starting with big "
D".
It's for deviation.
For example, for my place: 37.23°, -121.82° , deviation today is 14.4889,
it's changing about -5' per year