Typekit is built around web standards and their service gives designers and developers a subscription-based library of hosted, high-quality fonts to use on your websites. Typekit boasts some fancy large companies as customers including The New York Times, Twitter, and many others. They are also integrating the service into hosted platforms—such as WordPress, TypePad, and Posterous. Typekit has recently been acquired by Adobe.
I stumbled upon this when browsing a couple of web designers online portfolios, and I noticed a little icon in the bottom right-hand corner (the same as this site). For web designers and developers who want to use real fonts without hosting them themselves, Typekit is a great tool/service. I am continuing to integrate them across this site at the moment, and using the service has been a breeze. Thanks Typekit!