Windows Live Presence

From their site: The Windows Live Presence API is an HTTP-based API that returns a Windows Live Messenger user's presence using JavaScript Object Notation (JSON) or an image. The Windows Live Presence API can be used in conjunction with the Windows Live Messenger IM Control. A Web site can show a user’s presence using the Windows Live Presence API and let visitors send messages to the user with the Windows Live Messenger IM Control.
Windows Live Presence

AOL Open Mail

From their site: The AOL OpenMail API allows developers to create AOL Mail services on third party websites. Developers can use the OpenMail to access mail count and mail details. AOL, AIM and personal domain accounts are supported by the OpenMail API.
AOL Open Mail

Shopzilla

The Shopzilla, Inc. Catalog API provides access to the Shopzilla, Inc. inventory of catalogued products, merchant offers, and merchant ratings & reviews content through a query-based RESTful web service, responses formatted in XML or JSON|P. Managed through the Shopzilla Publisher Program, a CPC affiliate marketing program, publishers are able to monetize using this API. Users of this API are able to choose between two versions, each providing logic native to its corresponding Shopzilla, Inc. property: Bizrate.com or Beso.com. Bizrate API: Provides access to the entire Shopzilla, Inc. offer universe, exposing content from 8,000+ merchants. You would use this version to create a full comparison shopping site. Beso API: Provides the opportunity to create a style-based experience with a curated set of offers focused in soft goods categories. You would use this version to create a fashion-oriented shopping site. Both APIs provide access to the merchant ratings and reviews collected through the Bizrate Insights platform. International? APIs also available for the United Kingdom, Germany, and France.
Shopzilla

MySpace

The MySpace Developer Platform (MDP) allows developers to create applications that interact with MySpace members and their social data. With MDP you will be able to create compelling new products that integrate directly into MySpace pages and get exposure to millions of people around the world.
MySpace

PeopleAggregator

These APIs are available to any network implemented on top of the PeopleAggregator platform. See peopleaggregator.net for an example. From their site: PeopleAggregator brings social web features to existing software or provides a stand alone social network of your own. We've got source code available or we can build you a SaaS system to your specifications.
PeopleAggregator

Widgetbox

Our mission is to help people make and get widgets and apps for their social network profile, blog, or start page. Through our AppAccelerator, developers can easily convert their web widgets into standalone Facebook and Bebo applications.
Widgetbox

SesameVault

Upload videos, encode videos, tag videos, filter videos, and create reports. Ruby, PHP, and Javascript libraries are available.
SesameVault

dopplr

From their site: Dopplr lets you share your travel plans privately with a group of friends and colleagues whom you have chosen. It then tells you when people you know will be in the same cities. It also reminds you of people who live in the places you're planning to visit. The API is based on Google AuthSub. We intend to replace this AuthSub clone implementation with OAuth in the near future.
dopplr

MailChimp

Sync campaign stats and subscriber information between MailChimp and your database. This helps you download a list of unsubscribes to clean your inhouse lists, build client portals and pull campaign stats from MailChimp if you send emails on behalf of clients, aggregate and compile campaign stats, send "we also recommend this..." campaigns, and pass account status data to MailChimp so that only active members get your emails. [[http://www.mailchimp.com/tryit.phtml Get a Free Account Today!]]
MailChimp

Unfuddle

From their site: Provides developers with a very simple medium for creating new Unfuddle-based applications or integrating Unfuddle with their existing development workflow. It offers direct access to practically all the features of your Unfuddle account. Unfuddle is a secure, hosted software development environment and project management solution for small software development teams.
Unfuddle