Tannerite is a binary explosive that is readily available from the website Tannerite.com. It has gained notoriety in 2008 because of high-profile stories like these:
A "binary explosive" is an explosive made of two parts that must be mixed before it becomes explosive. In the case of Tannerite, the two parts are fairly benign prior to mixing. After mixing, they are explosive but require a great deal of shock (e.g. being hit by a bullet or triggered with a blasting cap) to initiate the explosion.
The chemical formula and mixing process is described here: What is Tannerite