There's a deep, dark, hidden Web out there: the Web of paid content. You probably run across it from time to time when you click on a link to an interesting-looking story and find that you'll either need to pay a few bucks to read the story, or subscribe to the site to get access. You won't see the paid Web on Google or other search engines, though: it's not in their interest to show you what you can't have.
Congoo is one way to bypass the content toll-takers. The company has done deals with hundreds of content providers and will give you access to a limited quantity of stories from each of them--generally up to five or six stories a month per publisher.
Many of the sites are newspapers, and frankly I don't understand why some papers charge for old stories and not the current ones. Nonetheless, if you want to read an archived story from the Financial Times or from a local paper like the The Bellingham Herald, Congoo has done the deals that will get you access when you need it (although one paid site that I'd like to see as part of the Congoo network isn't there yet: The Wall Street Journal). But more importantly, the system has access to stories from medical, business, and trade journals that are generally not accessible without a paid subscription. If you're researching a medical condition, you might be able to find important content that otherwise would not turn up in a search.
Congoo also can return articles from the Encyclopedia Britannica, if you like your reference materials old-school style (I'm sending my kids to Wikipedia -- because it teaches them not to believe everything they read).
The downside to Congoo is that in order to access the articles it makes available, you need to use the Congoo search toolbar (there are versions for Firefox and Internet Explorer). You might not mind this, since Congoo searches both its own database and Yahoo, but if you're hooked on another search engine, using Congoo means either adding a new toolbar to your browser for intermittent access to stories, or replacing the toolbar you're using now. The company is working on a toolbar-free solution, but for the moment it needs to run via the toolbar since that code is the gatekeeper that metes out paid content.
Congoo is free, which makes it a deal. The company makes its money displaying ads on its search result pages. In the future, it may offer paid services as well.
Congoo opens up big parts of the Web you might not otherwise see. If you can stand the fact that it requires a toolbar installation, it's worth using.