From immortal bloodsuckers and 19th-century forensics pioneers to flying suits of armor and an all-new breed of live-action 3-D, the essence of this year's hottest properties at Comic Con can be found deep in the past or far into the future.

"Twilight" proved to be the most rabid fan-feeding frenzy at last year's Comic-Con, and its sequel, "New Moon," based on the second novel in the vampire series by Stephenie Meyer, stands out among the savory offerings being shown through Sunday at the San Diego Convention Center.

Other highlights include "Tron," a reboot of the '80s sci-fi classic about computer programmers trapped in a digital world, Tim Burton's take on "Alice in Wonderland" and an early look at "Iron Man 2." James Cameron will also preview "Avatar," a futuristic adventure that promises a new level of 3-D based on technology the "Titanic" director helped develop.

Now in its 40th year, the festival began as a comic-book convention in 1970 and evolved into an expansive pop-culture buffet that includes video games, TV shows, major movies and A-listers from the worlds of film, television and publishing.

"It's the Las Vegas of conventions for this type of material," said Ellen Goldsmith-Vein, owner and chief executive of the Gotham Group and a veteran of 18 Comic-Cons. "It's an opportunity for fans to meet artists and buy artwork and see new stuff that's coming out. Plus it's really a festival — it's a circus in terms of the people who show up there in full regalia."

Costumed fans — a Comic-Con tradition — add spice to what's already an enthusiastic crowd. Visitors to San Diego's historic downtown area during Comic-Con might see Darth Vader at Rite Aid or run into Iron Man at the ATM.

The convention is like "the geek's Sundance or the pop-culture Sundance," said Gregory Ellwood, co-founder and editor-in-chief of the entertainment Web site www.Hitfix.com and a six-time Comic-Con veteran.

Megan Fox is to attend in support of "Jennifer's Body" and "Jonah Hex"; Robert Downey Jr. will be on hand for "Iron Man 2" and "Sherlock Holmes"; Peter Jackson is coming to his first Comic-Con to show off the latest film he produced, "District 9," and Cameron Diaz is set to promote her new thriller, "The Box." Sigourney Weaver, one of the stars of "Avatar," said she's excited to be making her Comic-Con debut.

"I've always wanted to go," she said. "For me, with all these between 'Alien' and 'Ghostbusters' and 'Galaxy Quest' and 'Avatar' now, it's an event I've been dying to go to for a long time."

TV fans will find plenty of appetizing options, too.

Kiefer Sutherland is to offer a glimpse into the new season of "24." The co-creators of "Lost" will share insights into the show's final season. The producers and cast of "Fringe" plan to present exclusive footage, and the people behind "Glee" will share a new episode of the new Fox show that debuted after the "American Idol" finale and picks up again next month.

"This is not what the founders of the Con thought about 40 years ago when they started this," said Ellwood, adding that fan reception at Comic-Con can help movies and TV shows find dedicated followings.

Admissions for this year's festival have been sold out for weeks.

"Donnie Darko" director Richard Kelly, who's bringing his new movie, "The Box," to the convention, said he has enjoyed Comic-Con as both a filmmaker and fan for nine years. He sees the growth of the festival to include properties beyond comic books as a boon for moviegoers.

"You've got to think it's a good thing for cinema, because it's given the fans more power," he said. "The studios are really listening, and they're really paying attention to what the fans think and what they want. Anything that empowers the people who really love movies is a good thing."