Watching TV shows when and where you want to is quickly becoming commonplace in a world awash with Hulu, TiVo, and iTunes. Yet if the fragmented media landscape is great for consumers, it's hell for advertisers. Now, big brands are turning back to an idea as old as P&G-sponsored soap operas -- hiring agencies to create entertainment designed to promote products. Only this time, companies are doing it via playful webisodes and websites and are also experimenting with alternative-reality games, or ARGs. These are like puzzles that build anticipation for a product release by sprinkling clues on the Web and in the real world. Spending on these forms of branded entertainment, as it's being called, grew 13 percent in 2008 to $25 billion, according to estimates from the research firm PQ Media. Here's how the leading players stack up:

42 Entertainment is a collection of game developers, artists, puzzle makers, theater folk, and writers. Its specialty is ARGs.

BREAKOUT WORK: "Why So Serious," 42's campaign for the Batman film The Dark Knight, started with several websites that were made to look as if they had been hacked by the Joker. Online clues led to a scavenger hunt through major cities; players who sent in pictures of themselves as the Joker were mailed copies of the fictional newspaper The Gotham Times.

BIGGEST CAMPAIGN: 124 million viewers

Kevin Townsend, founder of Science + Fiction, honed his skills as head of digital for George Lucas's Industrial Light & Magic. His forte is webisodes that pull in pitch-perfect Hollywood talent. For "The Rookie," an online series about a secret agent for Degree Men deodorant, he got veterans of 24 and Law & Order.

BREAKOUT WORK: In the Motherhood, developed by the producers of Friends, features Suave shampoo's target demographic: harried mothers. ABC picked up the online sitcom in March.

BIGGEST CAMPAIGN: 16 million viewers

Big Spaceship made its name building websites for movies like Bridget Jones's Diary. Now, it creates digital campaigns for the likes of Adobe, Corona, and Epson.

BREAKOUT WORK: Big Spaceship client HBO is known for giving viewers an intimate look at its characters. The Voyeur Project is a website on which apartment dwellers in 12 virtual New York City downtown apartment houses are shown going about their private lives in the style of Alfred Hitchcock's Rear Window. HBO also projected the site's content on the side of a real apartment building.

BIGGEST CAMPAIGN: 12 million viewers

Launched by creators of The Blair Witch Project, Campfire staged a mock heist at Audi's Manhattan showroom on Park Avenue. From there, the action went online and on TV, with a couple racing for their lives and a hit man in hot pursuit.

BREAKOUT WORK: For FiOS, Verizon's fiber-optic broadband network, Campfire produced a home-makeover show called My Home 2.0, in which Verizon tech geeks show homeowners the virtues of getting wired for digital. Verizon then organized block parties in areas eligible for FiOS.

BIGGEST CAMPAIGN: 10 million viewers

THE LINE: Brands are looking for ad agencies that have "experience pulling off things that haven't been done before," says Rob Reilly, creative director at Crispin Porter + Bogusky, the agency behind Burger King's viral Whopper Freakout. Given the huge success of its innovative campaign to promote The Dark Knight, ARG pioneer 42 Entertainment is a clear standout. But such blockbuster campaigns can be expensive to produce and do not always achieve the stellar results that millions of devoted Batman fans helped produce for this one. That's why Big Spaceship, with its scrappier approach, is a dark horse to watch.