The Skype Educator Network is provided by Skype to connect teachers with other teachers and resources through a searchable list. Teachers can create their own requests for other teachers to respond to as well.
The Skype an Author site provides a database of authors willing to Skype with classrooms. Organized alphabetically, each author provides a list of things they can talk about, appropriate age group, best times, and any other prerequisites. All authors are available for 15 minutes for free, but offer longer visits for a fee.