SAN DIEGO -- Grab your superhero costume and your autograph book. The 40th year of America's biggest pop culture convention opens today.

At Comic-Con International, many of the 125,000-plus fans wait hours -- sometimes overnight, sometimes in elaborate costumes -- for a seat in giant Hall H of San Diego's humongous convention center, where they can settle in during four days of panels that feature the stars and filmmakers of such anticipated blockbusters as "The Twilight Saga: New Moon," "Iron Man 2" and James Cameron's "Avatar," his first film since "Titanic."

If you're not there during the film and TV sessions tonight through Saturday, you might miss breaking-news moments, such as when Leonard Nimoy introduced Zachary Quinto as the new "Star Trek's" new Mr. Spock.

But if you're not in the even-larger Exhibit Hall at any given moment, who knows what free stuff might elude your grasp. There are enough giveaways to fill Warner Bros. signature huge canvas bags.

Comic-Con has evolved as a must-be-there site for genre fans because the TV, movie and gaming industries wouldn't miss their place in the spotlight, alongside the comic books that were the big show's launching pad.

The set-up allows publishers and studios to make an unfiltered presentation directly to the consumer. Attendees number a fraction of a first-week audience for most of the products on display here, but many are hard-core in their fandom, and they are avid users of the Internet.

Warner Bros. Television division felt the warm embrace of fans last year, when stars such as Emmy-nominated Jim Parsons sat down at the panel for the sitcom "The Big Bang Theory."

"We go through rigorous dialogue over each show and whether or not it should go to the Con," said Lisa Gregorian, who has watched the convention evolve in scope and variety during her seven years as vice president of worldwide marketing for Warner Bros. Television Group. Mythology-based series are "shoe-ins," she said. And "Big Bang," featuring geeky geniuses like Parsons' Sheldon, was a natural, too. "They reference everything from DC Comics characters, to 'Star Trek,' to video games, to World of Warcraft. Their world and the entertainment they consume in their world, it directly correlates with Comic-Con."

But that still didn't prepare Gregorian for the enthusiastic fan reception, which she described as "moving."

"It shows us the power of the connection between the fans and the characters in the show. You're reminded of that. Because we talk about it, but when you see it, and when you see it with thousands of people in a room ... I think for everybody, it's a very rewarding experience."

Warner Bros. opens Comic-Con tonight for the second year in a row. Last year, the studio brought the pilot for J.J. Abrams' "Fringe," which has been picked up for a second season on Fox. This year, three shows will try to cement a fan base: "V," based on the 1980s miniseries of the same name; "Human Target," based on a DC Comics character; and "Vampire Diaries." The latter will try to ride the coattails of the current vampire craze that includes HBO's "True Blood" and the "Twilight" film series.

With its "Twilight" panel at Comic-Con last year, Summit Entertainment got more than a hint of the avid fan base that awaited the movie's debut.

"Up until that point, we didn't know how big and how mobilized. It required a lot of fans to travel across the country to be there. Clearly, they were devoted; they camped out overnight, which none of us had seen before for films at previous Cons," said Jack Pan, executive vice president of marketing for Summit.

"It communicated to us this fan base was beyond anybody's wildest belief. That's when we knew that the passion from the core fans could really be spread to a mainstream audience, and that we did have a pop culture phenomenon forming. We also had all the major media outlets covering 'Twilight' really for the first time, and those that didn't have 'Twilight' on their radars certainly did after that."

Stars Robert Pattinson and Kristen Stewart, who were rocked by the response, should be prepared when they take the stage for the "New Moon" panel tomorrow.

"It's a very pure environment," Pan said of the very human reactions from the overwhelmed actors and their adoring fans.

Before the "New Moon" panel, the cast of Summit's "Sorority Row," the horror film shot in and around Pittsburgh last fall, have the stage. Pan notes that the captive audience provides a great showcase for the young leads, including Leah Pipes, Rumer Willis and Briana Evigan.

"They are very charismatic, and again, like the cast of 'Twilight,' these are up-and-coming actresses who mostly have not had major roles before," he said. "They'll be able to introduce a clip that has never been seen before and give the audience a taste of the movie that we haven't had the opportunity to get out through traditional TV, print and online publicity. So we certainly hope this will boost the profile."

A franchise that needs no introduction is George Lucas' never-ending space odyssey: Friday is "Star Wars Day," when the "Star Wars Spectacular!" will become the first panel filmed for TV, airing on the G4 network beginning at 2 p.m. Saturday.

Gregorian sees Comic-Con as a booster event for Warner Bros., embracing the chance to interact with fans by creating ways to put the company's products into their minds, hearts and hands. Giveaways at the booth include those Con-exclusive giant bags, and she's always looking for new ways to reach potential viewers.

For example, Gregorian says, Warner Bros. has a lock on promotions using San Diego's hotel keycards -- about 50,000 in 37 hotels.

"Last year I was walking with my girlfriend, who's been coming for years, she's in the digital division, and I said, 'I wish we could do something with these keycards. I mean they're cool and we like them and they're promoting our shows but ...' And she says, 'Why don't we do some kind of download?' So we made a deal with iTunes, and each card this year has a download code to download one of our series for free."

The wired audience and massive media presence at Comic-Con is another reason that the entertainment industry can't stay away. For better or worse, the minute something is revealed, it's a Tweet away from global recognition.