Google
In the Google Books search service, you can find information on most any book you'd care to mention. There are user reviews, keyword lists, and often a few pages of preview materials. But downloading the whole thing is typically limited to public domain works -- if you want to buy the darn thing, Google is happy to link you to Amazon.com
The WSJ says that this lost monetization opportunity is about to get captured. The upcoming Google Editions service will still include links to rival booksellers, but also lets you buy a digital copy right from Google, in an unencumbered format that should be compatible with nearly any e-reader on the market. Your Editions-backed books will be available in an online library connected to your Google login account, which makes a cloud service out of the whole thing.
If you can buy one book from Amazon, another from Barnes & Noble, and yet another directly from Google and then make them all available in a single, centralized location with minimal technical tinkering, the convenience should translate into a powerful market position for Google almost instantly. The service is expected to launch by the end of the year, stocked with "hundreds of thousands of titles for purchase, and millions more for free" right at launch. That's a delay from the originally planned launch in the summer of 2010, but getting the service out the door before the holidays would still give Google a chance to prove its mettle right away.
Given the retail successes of Amazon's Kindle, Barnes & Noble's Nook, and the Apple
Follow Google's digital adventures by adding the stock to your Foolish watchlist right now.