Gun Facts - Gun Control | Facts | Debunk | Myths
Gun Facts is a free e-book that debunks common myths about gun control. It is intended as a reference guide for journalists, activists, politicians, and other people interested in restoring honesty to the debate about guns, crime, and the 2nd Amendment.

GunCite: gun control and Second Amendment issues
Pretty much everything related to gun laws but not updated as regularly as it used to be.

ATF Online - Bureau of Alcohol, Tobacco, Firearms and Explosives
Lots of source information. Not a lot of interpretation.

Guns in the United States: Facts, Figures and Firearm Law
Good quick reference stuff

USA Carry - Your #1 Concealed Carry Resource and Community
Among other things, a good resource for CCW reciprocity info
Really more of a "gee whiz" kind of thing but a very simple resource for some really basic statistics
Link to really big image showing comparison of various rifle rounds ranged from (generally) least powerful to most powerful.
(FYI - #23 is what gets used in an AK-47. #26 is what gets used in an AR-15. #44 is essentially the same as a .308 Winchester)
A fantastic calculator for ballistics. Now, if it could only be adapted to portable devices.....