Like poets, comic book artists, and short-story writers, indie rock musicians sign on for a life of noble squalor and, at best, cult celebrity. They’re an ascetic order, whose rituals include performing at sweaty basement shows, sleeping on beer-splattered floors, and crisscrossing the country in cramped vans held together by little more than duct tape and positive thinking.

Given the shoestring approach of most indies, an album that sells 10,000 copies can be profitable, and throughout the 1990s, a release that sold 30,000 to 40,000 was considered a runaway success. The most popular indie rock bands of the era – Sunny Day Real Estate, Pavement, Built To Spill – topped out at around 100,000 albums or slightly more. It became an article of faith that an indie rock band simply couldn’t sell more than 100,000 records without access to MTV or commercial radio, which could only be had with major label backing.

In the last year-and-a-half, however, a handful of indie rock bands have broken through the glass ceilings of the genre, penetrating the formerly inaccessible worlds of television, movies, and commercial radio and posting sales numbers once thought impossibly out of reach.

Consider these recent sales figures: Bright Eyes’s album “Lifted or the Story Is in the Soil, Keep Your Ear to the Ground” (Saddle Creek) has sold 190,000 copies since its release in 2002, more than twice what their last album did, and their two recent singles ranked no. 1 and no. 2 on the Billboard Singles Chart.

The Shins’s latest, “Chutes Too Narrow” (Sub Pop), has sold more 250,000 copies, and thanks to Natalie Portman’s “It’ll change your life” endorsement in the film “Garden State,” their earlier album “Oh, Inverted World” (Sub Pop) is gaining fast.

Death Cab for Cutie’s latest, “Transatlanticism” (Barsuk), has surpassed the quarter-million mark, and the band recently signed to Atlantic Records.

But the most successful of this bunch is “Give Up” (Sub Pop) by the Postal Service, a collaboration between Death Cab for Cutie frontman Ben Gibbard and electronic artist Jimmy Tamborello (better known as Dntel).The album has sold 453,000 copies since its release in early 2003 and posted its best single week sales just before Christmas 2004. Sub Pop expects it to surpass the 500,000 mark in the next two months, making it only the second album in the label’s history to go gold. The first was Nirvana’s “Bleach.”

The success of grunge in the early 1990s radically transformed the relationship between underground and mainstream music. Ever since, major labels have hoped for – and in some cases tried to manufacture – another underground movement to once again spill over and transform pop. This impatience has produced several false “next-grunge” moments, of which emo and retro rock are only most recent examples.

What we’re seeing now is different in important respects. First, it isn’t an instance of hype anticipating sales; these records are performing, and that’s causing people to talk. Second, this isn’t even a “movement” in the typical sense.

“It’s not like emo, where you’ve got all these bands where there’s a defining factor,” says Jordan Kurland, manager for Death Cab for Cutie. “Arcade Fire, Bright Eyes, Death Cab: Aside from cheap records and depth of lyrics, there’s nothing that ties them together. Not a divinable theme like grunge, where it’s based around guitar and flannels.”

These changes in rock are part of a broader cultural shift: the indie-fication of popular culture. Artists who traditionally appealed to narrow niches are gaining a mainstream following – or rather, they are seeing their niches expand, even as the audiences for “traditional” outlets like network television and radio stations radically shrink. And unlike pop culture of the recent past, which concerned itself exclusively with the lucrative 12-to-18-year-old age group, this culture appeals more broadly: to 20- and 30-somethings as well.

Examples abound in all areas of pop culture. In movies: the box office success of “Napoleon Dynamite,” “Garden State,” “Sideways,” “Lost in Translation,” and the elevation of screenwriters and directors like Charlie Kaufman and Wes Anderson to celebrity status. On television: the appeal of “The Daily Show” and the crude brand of hipster comedy of “Chappelle’s Show.” In print and online: the popularity of publications like The Onion, Vice Magazine, and McSweeney’s.

Taken together, these represent an entire parallel pop culture, one that defines itself against the mainstream and, for generations of Americans, increasingly replaces it.

These cultural changes dovetail with changes in politics. Certain acts like Death Cab for Cutie and Bright Eyes benefited from the publicity they received this last year, barnstorming alongside the likes of Bruce Springsteen, Pearl Jam, and R.E.M. on the anti-Bush Vote for Change Tour. But more important than a shared political outlook may be the grassroots network that nurtures it.

The same Internet tools – blogs, meet-ups, Friendster-like communities – that made MoveOn.org a political force also fuel the success of independent music. Young people no longer look to the clerk at their local Tower Records for album recommendations but turn to their LiveJournals and Friendsters, to indie music sites like Pitchforkmedia.com and communities like MakeOutClub.com and SuicideGirls.com- a network in which indie rock is the coin of the realm.

Yet it isn’t always an either/or proposition; indie rock is also finding its way into mainstream entertainments. In the hit Fox teen melodrama “The O.C.,” Adam Brody plays Seth Cohen, a geeky hearthrob and one-man Death Cab for Cutie fan club. Not only have the band’s songs played during episodes; characters have argued over their music and given their CDs as gifts. “Music from the O.C.” CDs spread the gospel even further, introducing fans of the show to indie bands like Spoon, Interpol, and the Album Leaf.

“‘The O.C.’ has had an enormous impact,” says Kurland. “Two weeks ago [sales of Death Cab for Cutie’s album] went up 25% after Seth said their name a few times. We did an ad card – ‘featuring music by’ – after an episode, and we saw a jump in sales when there was no other possible explanation.”

“I think honestly a lot of it has to do with the coming of age of the kids in the mid-1990s,” says Tony Kiewel, the A &R (artist and repertoire) man for Sub Pop who signed both Postal Service and the Shins to the label. “People our age are suddenly in charge of the music on ‘The O.C.’ or are music bookers or whatever.”

Bands in this stratum may also be the primary beneficiaries of file-sharing and downloading, the same forces the major labels decry. Whether on iTunes or peerto-peer networks, it’s a short step from hearing about a band to actually hearing them – which is vital for bands and labels that can’t get themselves on commercial radio or MTV, or in many cases even into chain stores.

This is about the only way to account for a phenomenon like the Postal Service, which succeeded with little advertising or tour support (both members were too busy with other projects). “We have seen insane amounts of [free] downloads – 3 million on our site, averaging 125,000 a week,” says Sub Pop’s Kiewal. “It was no. 1 on iTunes. I have to assume that 4 million people have downloaded that band. We don’t have anything else that has done a tenth that much.”

The same democratizing force has transformed radio in recent years. Even as ClearChannel continues its homogenizing march through commercial radio, Internet and satellite stations (XM and Sirius) have sprung up. Today, indie rock (along with jazz, blues, bluegrass, and just about everything else) is available in places that never had the benefit of a good, land-based college or independent radio station. Local independent stations like KEXP in Seattle and KCRW in Los Angeles have found a sizable national and international following for their programming over the Web.

Once a band like the Postal Service, the Shins, Death Cab, Interpol, or Bright Eyes reaches a certain critical mass, commercial radio stations may even add them to their playlists, exposing them to a whole new category of listener. “Things tend to gather a momentum of their own at a certain point,” says Mac McCaughan, frontman for the 1990s indie stalwarts Superchunk and founder of Merge Records, home to the latest indie sensation Arcade Fire. “Now some radio stations that wouldn’t return our calls are going to sell these records.”

This snowball only applies to a fortunate few bands, however. For the rest, it is as difficult as ever. “In some ways, it’s harder and harder to sell records as a small band or a new or unknown band,” says McCaughan. “I think that unless you’re touring a ton and really getting yourself out there, there aren’t that many ways to let people know you’re around.”

Few in the indie-rock community anticipated this surge in sales, and nobody knows quite where it will end. “I think there is a peak somewhere, but I don’t know where it is,” says Jason Kulbel, label manager for Saddle Creek Records, home to Bright Eyes. “People are suggesting a gold record for Bright Eyes and that’s not something I’m saying we can’t achieve. Maybe a year ago I would have said, ‘No that’s not possible. You can’t sell that being a label with six employees in Omaha, Nebraska.’ But if you can sell 190,000 records, why can’t you sell 390,000 or 490,000?”

Or a million? Modest Mouse, a longtime favorite of the indie-rock crowd that signed with major label Epic a few years ago, scored a hit last year with their album “Good News for People Who Love Bad News,” which has sold more than a million copies to date and earned the band Grammy nominations for Best Rock Song and Best Alternative Music Album. Atlantic Records now hopes to replicate that success with Death Cab for Cutie.

Craig Kallman, co-chairman and COO of Atlantic, calls Modest Mouse “a very accurate blueprint for the path Death Cab is going to be on” but cautions that it probably won’t spark a whole new round of indie bands jumping to the majors.