FirearmsGuide offers a 20% discount on their software reference guide.
LINK: website

From their website:

The new Firearms Guide 4th Edition is a computer searchable firearms, air guns and ammunition reference guide that presents over 57,000 guns and ammo from 630 manufacturers worldwide and an amazing Schematics Library with over 4,300 printable gun schematics with parts lists from 360 manufacturers on DVD for PC or Mac!