At one time, perhaps, the taxonomy of indie kids could be limited to one definition, but as the word becomes increasingly bandied about in mainstream circles and the image thoroughly commodified by youth-orienting clothing chains, several distinct sub-types have emerged:

THE ART-POP KID: Generally shy and eccentric, probably a giant nerd with several guilty pleasure hobbies, the Art-Pop Kid legitimately loves the music itself and the spirit of the subculture, but maintains a protective distance from the culture itself as to not be wholly associated with it and its various hanger-ons (see below). The Art-Pop Kid thinks the music is important, he has a very Romantic sensibility, and is legitimately upset/shocked when outsiders accuse him of merely hugging trends. Seventeen years ago, the Art-Pop kid was in someone's basement, listening to the early incarnation of indie rock, and wondering what to get his girlfriend for her birthday.
ASSOCIATED ARTISTS: Beat Happening, Robert Pollard, Liars

THE AVANT-POP KID: Like the Art-Pop Kid but more confident and probably a little crazy. The Avant-Pop Kid doesn't so much look down on the mainstream for lacking substance, so much as he or she just exists in their own bubble, totally oblivious to the realities of the outside world. Seventeen years ago, the Avant-Pop Kid was shooting heroin, discussing Baudrillard with hobos at the bus station, and rolling their paint-slathered bodies around on a canvas.
ASSOCIATED ARTISTS: Gang Gang Dance, Throbbing Gristle, Xiu Xiu

THE FAG-POP KID: Generally upper class and owning their own parent-bought Scandinavian car, the Fag-Pop Kid is really nice and honest, just very dull and shallow. However, he or she doesn't think this, and will earnestly discuss dull, unimportant art (see: Wes Anderson, Victor Hugo, Conor Oberst) for hours at a coffee shop without ever broaching anything even remotely resembling an insight. Not coincidentally, they like their music soft and pretty, and usually prefer their art to deal with the melancholy of upper class suburban life. Seventeen years ago, the Fag-Pop Kid was listening to Tracy Chapman, thinking about joining the Peace Corps, and working on their Sociology degree.
ASSOCIATED ARTISTS: Belle & Sebastian, the Shins, Death Cab for Cutie

THE HANGER-ON: Frat kid in a novelty t-shirt, trucker hat, generally seen drinking Pabst Blue Ribbon with a girl ironically (or so she thinks) wearing short-shorts and a Hooters t-shirt. The Hanger-On might have a few mp3s from faux-indie bands like the Killers, Franz, and Daft Punk, but as a whole, he doesn't give a shit about anything other than the image. Keep in mind, he is not interested in the culture itself in any sense, just the image. As soon as Abercrombie and Fitch change their marketing campaign, they'll move on to gutting the next subculture of the hour. Seventeen years ago the Hanger-On was wearing pastel yellow sweaters, snorting coke, and voting for Ronald Reagan.
ASSOCIATED ARTISTS: The Killers, Franz Ferdinand, latter-day Modest Mouse

THE HIPSTER HARLEQUIN: A more highly evolved form of the Hanger-On, the Hipster Harlequin has slightly better taste and some grasp on the underlying ideas and spirit of the subculture. However, the Hipster Harlequin is, ultimately, all about appearances, and usually spends more time and money shopping for vintage clothes than listening to music. The Hipster Harlequin will discard their persona as soon as they end up in their inevitable cubicle career. Seventeen years ago, the Hipster Harlequin was thinking about spending a year in London before finishing his or her theater degree.
ASSOCIATED ARTISTS: The Yeah Yeah Yeahs, the Dandy Warhols, Dresden Dolls

THE POP HISTORIAN: Completely removed from the culture itself, the Pop Historian sits at his computer all day, downloading gigs of music, and tearing through it rapidly in an effort to acquire an encyclopedic level of knowledge. While the Pop Historian does legitimately love the music, he is the extreme manifestation of the more nerdy tendencies of the Art-Pop Kid, and despite loving music about relationships, has likely never had nor actually desires a close relationship with a member of the opposite sex. The Pop Historian is the most likely to get angry and flustered when discussing music, and on account of poor interpersonal skills, is likely to indirectly belittle others in a frantic effort to demonstrate the breadth of his or her grasp on pop history. The Pop Historian is also the most likely to proclaim a love for various forms of ethnic music to which he has no cultural ties, such as rap, R&B, or Thai-pop. Seventeen years ago, the Pop Historian was going to McDonald's to enjoy a Big Mac after looking for vintage jazz records at a rummage store.
ASSOCIATED ARTISTS: Devo, Stevie Wonder, the Olivia Tremor Control

THE REFORMED PUNK
A punk, real or fake, at a prior time in his life, the Reformed Punk listens to some indie music, but unlike the other varieties of Indie Kid (with the exception of the Hanger-On and, on some occasion, the Pop Historian), is very energetic and even aggressive. The Reformed Punk still retains a lot of rage from his past life, and though he now openly bears his soft side, he still prefers his music to have an edge. The Reformed Punk usually still dresses like a punk, but when asked about the genre, will usually lament that punk has been murdered by some perceived flaw in the culture. Not surprisingly, his old friends don't really like him anymore, and he's always eager to hang out and will drive you to the donut shop at 4 AM. Seventeen years ago, the Reformed Punk was getting bludgeoned into unconsciousness at a Black Flag concert (and loving every minute of it).
ASSOCIATED ARTISTS: Joy Division, Les Savy Fav, some grindcore band they still bear affection for