NEW YORK (CNN/Money) - When the clock strikes Halloween this Friday, don't be surprised if you find Neo, Roxie Hart and Captain Jack Sparrow asking "Trick or treat?" rather than the ghost, the ghoul and the goblin.

The "Gorilla Aloha" costume available at Party City and BuyCostumes.com.

If you haven't guessed already, Halloween is getting a heavy dose of Hollywood this year, with the hottest selling costumes inspired by a few blockbuster hit movies including "Matrix Reloaded," "Chicago" and "Pirates of the Caribbean: The Curse of the Black Pearl."

"The influences have shifted from last year's soldier and fireman themes to costumes from the recent popular movies," said Scott Wentworth, a vice president at the retailer Party City (PCTY: down $0.54 to $14.00, Research, Estimates).

Spiderman and the Hulk are the two hottest costumes at Party City stores, Wentworth said. "Spiderman is No. 1 right now even though the movie came out last year. For girls, it's the Disney princesses and the Barbie Rapunzel and Swan Lake costumes."

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Halloween is the biggest sales event for the Rockaway, N.J.-based retailer of party goods, which has 497 stores across the country. With just four days to go, Wentworth said he's already anticipating strong sales compared with last year.

"Couples costumes and humorous costumes are also pretty big this year," Wentworth said. "As we get closer to Halloween, that's when people really get creative. One of our popular adult costumes is the 'Glorilla Aloha'. It's a gorilla wearing an Hawaiian skirt and a flower lei."

Meanwhile, the Cartoon Network's "Justice League" superhero team, including The Flash, Wonder Woman, Hawkgirl and Green Lantern, are hot at e-tailer BuyCostumes.com.

The Cartoon Network is part of Time Warner (AOL: Research, Estimates), which also owns CNN/Money as well as other properties.

"The Flash is a real standout so far in the 6-to-10 age group. People are going wild for that costume," said Diana Krohn, director of marketing for BuyCostumes.com.

The company claims to have the largest selection of costumes on the Internet, about 25 percent of the market, and gets 1.2 million visitors a week leading up to Halloween. Its Halloween sales this year have already doubled over last year.

"The Cat in the Hat, Sponge Bob, and the Harry Potter and Lord of the Rings characters are big too," said Krohn.

By contrast, it's the old standbys fueling costume and mask sales at Costume Holiday House.

"We've noticed that it's back to the favorites, like a ghost, a clown or an angel," said Gregg Kerns, president of the regional retailer based in Ohio.

"For adults, our biggest seller is the 'plug-in socket' costume," he said. "You get two costumes for the price of one."

Political costumes usually get the thumbs down from consumers when it's not a presidential election year. But this year, retailers say, the Arnold Schwarzenegger mask is generating interest.

But shoppers may be hard-pressed to find the masks. "By the time Arnold got elected, it was already too late for us to place orders," said Party City's Wentworth.

According to the National Retail Federation (NRF), Halloween retail sales are expected to fall to $6 billion this year, down 15 percent from last year.

Industry watchers and retailers say they're still hopeful for a late sales surge.

"Halloween this year falls on a Friday. That should be helpful for retailers because the party carries into the weekend," said Richard Hastings, chief retail analyst with Bernard Sands.

"We had a strong back-to-school season and discretionary spending on low-priced items has trended higher," Hastings said. "These are good indications for Halloween, which typically sets the tone for the rest of the holiday shopping season."

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Wal-Mart (WMT: Research, Estimates), the world's largest retailer, said in its weekly sales update Monday that Halloween sales were on track.

At discounter Target (TGT: Research, Estimates), Ozzy Osbourne, Matrix and Barbie-inspired costumes are leading the pack.

"People are also buying costumes for their pets. Halloween decorations like the sugar-textured lights, skull lights, the flying witch and pumpkin-carving kits are doing very well," said Paula Greer, spokeswoman for Target Corp.

For more on costumes for pets this year, click here.