Nitrogen can hybridize in the sp2 or sp3 state, depending on if it is bonded to two or three atoms, respectively. With both sp2 and sp3 hybridization, there is a pair of lone electrons on the nitrogen atom that does not participate in bonding.
Ammonia and methylamine are two examples of compounds in which nitrogen is hybridized in the sp3 arrangement. Pyridine is an example of nitrogen hybridized in the sp2 arrangement.
In addition to nitrogen, oxygen and sulfur also undergo hybridization. Oxygen has a sp3 hybridization when it is bonded to two atoms and there are two lone pairs of electrons on the oxygen atom. Sulfur has an sp3 hybridization when bonded to two atoms.