The main excitatory neurotransmitters are glutamate, acetylcholine and norepinephrine (and epinephrine), while the primary inhibitory neurotransmitters are GABA and serotonin. Serotonin is actually a complicated one and is more accurately called a neuromodulator because, depending on the context, can be either excitatory or inhibitory. Despite this, by far the most common neurotransmitters in your nervous system are glutamate and GABA.
