From Kathy Schrock-http://www.schrockguide.net/critical-evaluation.html
.com - Commerical
.edu - Educational sites (faculty and student pages can use this also, so be sure to double check!)
.org - Nonprofit groups or organizations (usually but not always anymore)
.us, .uk, .de, etc - Country codes (tell you the country of origin for the website but doesn't tell you if it's personal or professional)
.mil - Military based website