Ballistics Tools
Berger Bullets Stability Calculator

Berger is known for their quality bullets, particularly their long range offerings.  The calculator is geared toward their products, but it can be used successfully for any bullet as long as you have the appropriate criteria.
Below are links to online and downloadable tools for calculating various data concerning bullet stability, trajectory, drag functions, power factors, internal and external ballistics, to creating range cards, etc.
JBM Ballistics

A large collection of ballistics calculators for everything from stability to trajectory.
Hornady Ballistics Calculator

A nice calculator that generates bullet velocity, energy, and drop across maximum range and distance intervals (down to 25 yards).  It takes into account sight height, shooting angle, and wind speeds and angles.  The calculator creates a conveniently formatted output that can be printed for reference.  Two calculators are offered; standard and 4DOF.
Close Focus Research Internal Ballistics Calculator

A downloadable Microsoft Excel spreadsheet containing editable fields to assist in determining chamber and barrel pressures for a given combination of barrel diameter, velocity, and bullet weight.  Reverse calculations are also included.
Gordon's Reloading Tool

A freeware graphical tool for all things ballistics related.  GRT is incredibly detailed and rivals the top tier commercial ballistics programs on the market.  It has an active community of users and database updates seem to be frequent. Download requires you to register on the site, but it is free.  Highly recommended!