Formaldehyde, Ammonium Sulfide, and Hydrogen Peroxide are used to make HMTD, a primary explosive.
http://www.aristatek.com/newsletter/0512December/TechSpeak.aspx
Just a mildly interesting use for formaldehyde.
Oops! Should be Ammonium Sulfate, not Ammonium Sulfide...
Sorry about that..