In his latest book Free: The Future of a Radical Price

 Chris Anderson lists fifty examples on free business models organized into three groups, Direct Cross-Subsidies, Two-sided markets, and Freemium. Below you have the list for free, that I hope Chris doesn't mind. Buy the book to get examples for each + the rest of the book (Freemium):

Free 1: Direct Cross-Subsidies - Any product that entices you to pay for something else

Give away services, sell productsGive away products, sell servicesGive away software, sell hardwareGive away hardware, sell softwareGive away cell phones, sell minutes of talk timeGive away talk time, sell cell phonesGive away the show, sell the drinksGive away the drinks, sell the showFree with purchaseBuy one, get one freeFree gift insideFree shipping for orders over $25Free samplesFree trialsFree parkingFree condiments

Free 2: Three-party markets - A third party pays to participate in a market created by a free exchange between the first two parties

Give away content, sell access to the audienceGive away credit cards without a fee, charge merchants a transaction feeGive away scientific articles, charge authors to publish themGive away document readers, sell document writersGive woman free admission, charge menGive children free admission, charge adultsGive away listings, sell premium searchSell listings, give away searchGive away travel services, get a cut of rental car and hotel reservationsCharge sellers to be stocked in a store, let people shop for freeCharge buyers to shop in a store, stock seller merchandise for freeGive away house listings, sell mortgagesGive away content, sell information about the consumersGive away content, make money by referring people to retailersGive away content, sell stuffGive away content, charge advertisers to be featured in itGive away resume listings, charge for power searchGive away content and data to consumers, charge companies to access it through an APIGive away "green" house plans, charge builders and contractors to be listed as green resourcesFree 3: Freemium - Anything that is matched with a Premium Paid VersionGive away basic information, sell richer information in easier-to-use formGive away generic management advice, sell customized management adviceGive away federal tax software, sell stateGive away low-quality MP3s, sell high-quality box setsGive away Web content, sell printed contentGive away online games, charge a subscription to do more in the gameGive away business directory listings, charge businesses to "claim" and enhance their own listingsGive away demo software, charge for the full versionGive away computer-to-computer calls, sell computer-to-phone callsGive away free photo-sharing services, charge for additional storage spaceGive away basic software, sell more featuresGive away ad-supported service, sell the ability to remove the adsGive away "snippets" sell booksGive away virtual tourism, sell virtual landGive away a music game, sell music tracksFree 4: In the book Chris also mentions a fourth type of Free that is not listed as it is not considered a business model: Nonmonetary Markets. An example that comes to my mind is to spend nights writing a blog without advertising to build a reputation, continuously develop ideas and concepts, keep yourself updated in a field, get feedback, and get into contact with smart individuals...

Download the audio book here: Free: The Future of a Radical PriceEnjoy!