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.

The site also ranks films with the "Tomatometer," which averages at least 50 or 60 reviews for an overall consensus. Rotten Tomatoes has become more than just an objective film-o-meter: with more than 100,000 titles and 360,000 review links ripening in its database, it's also an online resource for movie buffs.

Paint by Mood

Home decor icon Debbie Travis recently paired with Canadian Tire (Canada's original home improvement and auto store) to launch a new paint collection that eliminates the guesswork in choosing a wall color. Customers pick from four moods—nostalgic, calm, dramatic, cheerful—then choose a paint color that will evoke that feeling. There are approximately 80 colors in each group, plus 12 whites imbued with the palest hues of cream, blue, pink, lilac and green. The collection also includes practice pots with a built-in brush, so customers can pre-test the colors at home on a four-square-foot wall area.

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As consumer choice continues to swell, filters will gain even more market significance. The niche will rule. For example, homogenized, one-size-doesn't-fit-all radio stations are slowly being replaced by a musical buffet that listeners can download, customize and access at their convenience in podcast form. Get ready, folks, iTunes is just the start of this musical revolution. When the options grow wider, our focus naturally narrows to find the perfect fit.

Here are some lessons and questions to help you establish powerful filters for your brand:

1. Create filters in both "practical" and "passion" categories

Progressive Insurance has made it easy to filter through the benefits of all the available insurance offers. It's a welcome solution for a boring, yet necessary purchase. On the other end of the pendulum swing, fans will spend hours and days consulting filters in their passion categories, including books, fashion, music, gaming, travel, sports, collectables and politics.

2. Build a forum for customer opinions

How can you gather and leverage customer opinion data? Think about how brands like eBay, Amazon and Epinions have made minor celebrities out of their top reviewers.

3. Develop an influential insider

Consider creating an internal brand personality who shares her favorite purchases. For example, a travel company could profile its CEO and ask her to share favorite vacation destinations, packing tips, luggage criteria and the best ways to re-book a canceled flight or avoid travel headaches.

4. Filter out the unnecessary

Sometimes, knowing what not to buy is more valuable than information on what to purchase. The trusted author of The Girlfriends' Guide to Pregnancy has released a shoppers' guide to steer new moms through the dizzying array of products available for their little ones. New moms appreciate the scoop on what's essential to buy new and what's OK to pick up used or to just forget altogether.