Big.com is a search engine from Bill Gross of Snap that makes your search results enormous. The rumor is that Snap tested out big fonts and found they were a hit with seniors - they decided to spin off the idea in the form of Big.com. The results are powered by Ask/Teoma and come in three flavors: big, bigger and biggest.
Big.com also distributes a free toolbar for Internet Explorer called the Web Magnifier: this allows you to increase the font size in IE and search Big.com from within your browser. However, the utility here may be limited: Opera and Firefox users can already magnify fonts in the browser, while IE7 beta also includes the feature. Nonetheless, with such huge ads, the clickthroughs will likely be much higher than conventional search engines.
It's an imaginative use of a great URL, but you've got to wonder whether they'd make more by simply selling off the domain name.