The wall of removed comments is a little intimidating, but I'll take a stab at this none the less.

So, coffee.

I love coffee, and being a student of the Middle East have long been interested in the beverage's history. An internet search for the answer to your question will likely return a story about a 9th century Ethiopian farmer named Kaldi who discovered the plant. To the best of my knowledge, this story is absolutely false. Although I can confirm that the story is quite popular among Ethiopian co-workers of mine in the past. Another thing you will likely see is that the coffee plant is native to Ethiopia's Harrar region. While Harrar coffee is certainly very exquisite, I believe this information to be inaccurate as well, though I will not speak as firmly against it since I'm neither a botanist nor biologist. At any rate, it does run against my knowledge of the plant. The pairing of origin story and location strikes me as nationalist legend rather than fact.

So, if it's not from 9th century Ethiopia, where is it from?

Well, the earliest mention is likely in Arab chronicles circa the turn of the previous millennia. The main varietal of coffee, arabica should give us a clue to its origin as well. The coffee plant is a native species to the geographically isolated Yemeni region on the south side of the peninsula. The plant, and its invigorating properties were popular among the Sufi communities in and around Mocha. Their cultivation and preparation was highly regarded, and eventually Mocha became the center of the coffee trade which beans known for having a distinct flavor. When coffee was introduced to Europe during the Renaissance period, Mocha beans would have been highly prized and fairly expensive. After chocolate was introduced from the new world, mocha came to be a chocolate-coffee blend, allowing the unique flavor of Mocha beans to be replicated with beans of a much more diverse origin.

Yemen is closely connected to the Horn of Africa both in flora and in human movement and trade, and that region of Africa (Sudan, Ethiopia, Eritrea, Somalia, and Djibouti) has had coffee since before we have written record of the area. The plant grows across the region, and is consumed heavily and sometimes ritualistically in all of those countries. The oldest coffee (berry at first, later bean) preparation technique is to add coffee to a kettle of cool water, and heat it over a flame until it froths up. This is still the traditional method of serving coffee in Ethiopia, and I have been told in Sudan as well. Other methods, such as the repeat boiling of Turkish coffee, or the hot water bath of French coffee came later.

So... yeah.

Non-academic sources:

Espresso Coffee: The Science of Quality - Illy and Viani

The History of the World in Six Glasses - Standage

I apologize for the secondary source, it's not my area of study, but the information (primarily drawn from the first text) fits with academic and first-hand sources which I am familiar with (including my personal experiences and knowledge). May the mods have mercy. =)

I refer to a few sources here to add to what has already been said.