Y'all probably know what an ion channel is, having read the section on neurobiology basics. At least I hope you've read it. Ion channels are important in regulating the voltage of neurons and act relatively quickly compared to most receptors. Some ion channels actually are activated by linked receptors (these receptors are known as "ionotropic" receptors).
Ion channels are popular targets for antiepileptic drugs such as lamotrigine (US: LAMICTAL) and carbamezapine (US: TEGRETOL), the idea being that if an ion channel is blocked, the cell is less likely to transmit a message, lowering the risk of having an epileptic seizure.
Ion channel drugs are often used to treat bipolar disorder, as well. Officially, per FDA regulations, lamotrigine is one of the four approved drugs for maintenance treatment (i.e., taken every day regardless of your mood) of bipolar disorder. (Just FYI - the others are the ancient lithium and the atypical antipsychotics olanzapine (US: ZYPREXA) and quetiapine (US: SEROQUEL).) For the simple quashing of mania, carbamezapine (US: TEGRETOL; EQUETRO), as well as the valproic acid/valproate family (US: DEPAKENE, DEPACON, and many others) are also approved.
Now you know why they abbreviate it "GABA"! This neurotransmitter is generally known as a "calming" neurotransmitter that prevents signaling between neurons. It's no surprise that drugs that are pro-GABA (e.g., GABA agonists) can have the capability to prevent epileptic seizures. GABA drugs (especially gabapentin, aka NEURONTIN) have also been used in the treatment of various pain syndromes, especially those caused by nerve damage (neuropathy).
GABA is also the target of most prescription sleep aids and some anti-anxiety drugs. The benzodiazepine class of drugs is an older but still popular treatment option in anxiety and insomnia disorders.
Some very well-known examples of "benzos" include clonazepam (US: KLONOPIN), triazolam (US: HALCION), and perhaps our favorite, diazepam (US: VALIUM). The way benzodiazepines work, IMO, is pretty cool, since part of the pro-GABA process involves the drug pulling together 4 GABA receptors and creating its own little site to stick to!
In addition to "benzos", the newer "atypical hypnotic" sleep aids may also target GABA. Examples of these drugs include zolpidem (US: AMBIEN), eszopiclone (US: LUNESTA), and others.
NMDA (chemical name: N-methyl-D-aspartate; again, like GABA, you can see why it's abbreviated!) is like the opposite of GABA: Instead of calming messages, it enhances them. NMDA receptors (and of course, the neurotransmitter NMDA itself) are important in changing our neuronal pathways (presumably by destruction of old, "unnecessary" synaptic connections... pretty much the mental equivalent of road construction). However, NMDA in excess is particularly neuro-toxic, and that's why NMDA antagonists are becoming popular. For example, the drug memantine (US: NAMENDA) is used for the treatment of dementia in Alzheimer's disease, and the similar amantadine (US: SYMMETREL) is used to treat Parkinson's disease. Dextromethorphan, the active component in most OTC cough syrups (such as ROBITUSSIN), also has an NMDA antagonist effect.
The above was just a summary. For all intents and purposes, I pulled the above information out of my arse without really looking at authoritative sources. I'll be looking more seriously into these topics with the use of published sources (and of course, citations here) when I get the opportunity to write up the full version of this topic.