Gemini - the very, very, very first air sign; the most duplicitous, the most facetious Air sign (or zodiac sign in general) with an innate child-like, mischievous attitude towards life (they're playground) - they can either be serious (combined with this mischievous personality trait) or extremely light-hearted. They infuse their inappropriate (sometimes crude) sense of humor into situations to get certain reactions out of people and make life seem and feel less /dull./ Shaking things up every once in a while is healthy for a stereotypical Gemini who is quick on their feet, dexterous, active, witty, and silver-tongued. No one does things as good and as fast as a stereotypical Gemini - at least in their eyes. They feel unique in this way. Honestly, people either get them, or they simply just don't (and I don't think they care). They are the most "airy" Air sign because they're sociable, opinionated, highly, highly, highly, intelligent (MORE than they let on, believe me) fickle, and they like to keep all their options open. They are considered the Blind optimists of the Air element.
Libra - the second air sign; the most disarmingly charming Air sign with a /natural likeability/ factor that makes them popular among their peers (no matter how much you may hate one for some reason, people are compelled to like them for something); very easy-going, non-confrontational, and more importantly, most Libras are /patient/ and slow to anger - this is what causes them to inevitably be likeable. They have more patience to put up with (excuse my language) other people's sh*t. :) And they always deal with serious situations in a positive way by looking for alternatives and staying composed. They sometimes encourage other people to do the same. Also, they are natural romantics who either enjoy being pursued or enjoy pursuing others. But they do this by playing their cards right - which is essentially their approach to life. They somehow figure out the whats, when's and the how's. Like I said, they're probably the most likeable Air sign. Also, regardless of how superficial some may seem, they simply want the best and the finer things in life. They are therefore considered the Idealistic optimists of the Air element.
Aquarius - the third, and final air sign and the most complicated. But, they are also the most visionary Air sign with the ability to set trends and inspire others to be quirky, different, cool, and to let loose. The stereotypical Aquariuses have an off-beat, unpredictable personality. And while they may come across as cold and aloof sometimes, they are surprisingly (emphasis on surprisingly) very, very, very passionate about things and /spontaneously/ lively (especially at times when you don't expect them to be.) But it's not just anything that they are passionate about. They are passionate about things that are by no means considered trivial. Instead, they are passionate about things that actually /matter./ It's interesting because passion isn't necessarily synonymous with Aquarius - we usually associate the word with their opposite sign, Leo. The difference is: Leo is a fiery passionate zodiac sign (exuberant and uplifting) , and Aquarius is passionate but somewhat icy at the same time (polarizing and intimidating, because of their intellectual prowess). They're an intelligent bunch, and, unlike some of the other zodiac signs, they like to challenge other people to /think/ in a different way (maybe in a more abstract way) and to apply knowledge. Oh, and let's not forget about their tendency to be /extremely/ (maybe unintentionally) aggressive when provoked to anger - I repeat, they. don't. play. But, on a more positive note - because Aquariuses fight so hard for their identity and individuality, they refuse to give away all of themselves in personal relationships and dislike entertaining the idea of settling down and committing to another individual. Therefore, they are considered the Guarded optimists of the Air element. They don't play it safe, but they don't get /too/ ahead of themselves.
And that right there are your 3 Air signs - sociable intellectuals with a need for intellectual stimulation when dealing with others and the world at large.
Edit:
Oh yeah, my Ex is an Aquarius.