A few weeks ago, I met my musical match made in paradise.

I was surfing the Apple iTunes music store when I stumbled onto the playlist section—a space where musicians, celebrities and the average music lover all list their favorite songs and artists. It's a digital version of that great mix tape your best friend passed along to you in high school. Minutes later I was gaping, mouth open, at a playlist created by someone who shares my taste to the letter. I loved every song and bought the whole playlist.

The iTunes playlists are a perfect example of marketplace filters—people, editors, reviewers, curators, celebrities and experts who pre-select the good stuff and screen out the not-so-good dregs. How many times have you bought a CD because you loved one song, but ended up hating the rest of the disc? Those days have passed. The iTunes Music Store has already sold more than 400 million songs (at 99 cents each) and offers more than 1.5 million tracks for customers to preview, buy and legally download. Apple has hit a homerun with iTunes, and other industries are learning from its simple, flexible and highly participatory format. It's the ultimate music filter.

In a world that's increasingly inundated with massive amounts of choice, filters are a critical market phenomenon. Consumers rely on trusted filters to sift through the raw data and identify the top picks. As a result, many savvy brands are learning to build filtering mechanisms into their brands, their products and Web sites, while also giving consumers a forum for voicing their opinions and providing recommendations to others.

In today's global marketplace, it feels good to be "in the know" and to avoid costly and frustrating purchases.

If you're eager to attract more women customers, filters are smart business. Research shows that women actively seek more peer and expert recommendations than men before making a purchase, and they also conduct more research. When you build filters and filtering forums into your brand, women will respond enthusiastically with their wallets.

Need some more examples? Here are some innovative market filters attracting loyal fans and customers.

The Ultimate Insider

One word: Oprah. She recommends jeans, bras, books and everything in between. Women trust her opinions because they're not based on product placement or paid advertising. Oprah picks what (and who) she loves and passes it on. Her choices have enormous market sway. Oprah's filtering role is even more powerful because she gives her audience access to other insiders—whether a medical expert on menopause, an FBI agent who reveals how to spot a stalker or outspoken Brits who tell us What Not to Wear.

News & Gossip Guru

A true Web pioneer, Matt Drudge has earned a huge following for covering—and uncovering—news, events, tips and rumors before they surface in mainstream media outlets. Drudge became a household name in 1995 when he exposed former President Clinton's affair with Monica Lewinsky, and the Drudge Report site now generates more than 100 million pageviews a month. His methods may be controversial and some journalists say his news leans toward glorified gossip, but the Drudge Report has become a media force to be reckoned with—a clear example of how ordinary people can gain fame as information filters.

Consolidated Expert Opinion

When it comes to movies, everyone's got an opinion. So whom do you trust? Over 2.7 million readers a month visit the Rotten Tomatoes Web site for a broad sampling of critical opinion. Created by movie buff Senh Duong in 1998, Rotten Tomatoes is "committed to saving its readers time and money" by gathering reviews from a wide range of print and online critics, then separating their opinions into either "fresh" or "rotten" categories. Visitors can read brief excerpts from each review and follow links to the full text.