The Calais Web Service automatically creates rich semantic metadata for the content you submit – in well under a second. Using natural language processing, machine learning and other methods, Calais analyzes your document and finds the entities within it.

Searchmonkey bridges the gap between Beagle (simple interface, large search net) and find/grep (powerful searching, small search net). A fast, real-time search engine for displaying regular expression matches (both file name and content) across multiple directories. Written in Gtk2, it is highly portable, runs on Linux, and ports are available on FreeBSD, Windows and MacOS.

The Kannuu SDK is for developers interested in developing Kannuu based applications for one or more of their supported device platforms. The SDK is geared toward content discovery.

Access essential information about a specific business location including SIC codes, ownership, annual sales revenue, number of employees, and more.
Additional location-related API's:

MapPoint API

NAC Geo-services API

The JobCentral XML API can provide free and easy job content to websites without the need to bulk up on servers or develop search technology.
Additional job-related API's:

Indeed API

Executive Decision Makers Database API

The Google Book Search Book Viewability API enables developers to: Link to Books, thumbnails, and previews; Know whether Google Book Search has a specific title and what the viewability of that title is.
Additional book-related API's:

BookMooch API

ISBNdb API

O'Reilly Safari API

The Callfire API allows you to run a Call Center Connect campaign. You can control the popup screen and the way to collect data and get to the next call and more.
Additional phone-related API's:

StrikeIron Do Not Call API

Basic Option Pricing API

Real Time Telephone Verification API

The BD Live developer disc includes sample code, definition of available API’s and allows for collaboration. This includes the ability for developers to download each other’s applications to their home theater. The API's allow the quick creation of user-friendly DVD-like experiences.

Notches is a free, open, universal platform for reviews. The platform does normalization, entity aliasing, summarization, personalization, spam prevention, gaming detection, and recommendations and provides total access to the database via the API.
Additional Reviews-related API's:

Yahoo! User Product Review API

QuarkRank API

Yelp API

Orange now offers several APIs for all types of Web 2.0, SaaS and Social Network solutions.
Additional Social Network-related API's:

Open Social API

Facebook API

Digg API

Translate and detect the language of blocks of text within a webpage using only Javascript with the AJAX Language API.
Additional AJAX-related API's:

JSMX API

Ajax.NET API

Atlas API

Google AJAX Feed API

BookMooch is a community for exchanging used books. BookMooch lets you give away books you no longer need in exchange for books you really want. All the API calls support XML output, by adding &o=xml on the GET url line.
Additional book-related API's:

ISBNdb API

O'Reilly Safari API

The Amazon FWS API allows you to automatically process shipments to Amazon and then out to customers. This functionality is contained in two key APIs.
Additional API's from Amazon:

Amazon Simple DB API

Amazon Flexible Payments Service API

Amazon E-commerce Service API

Amazon Elastic Compute Cloud (EC2) API

The Callfire Voice Broadcast API allows you to perform various voice broadcast campaigns. Send a broadcast out to the phone numbers you specify. The sound file provided will be played back to live pickups and be left as a message on answering machines.
Additional voice communication-related API's:

PhoneNotify API

StrikeIron IVR Voice Notification API

SpokenBuzz API

NAC Real-Time Geo-Services Suite provides real-time geocoding, reverse geocoding, mapping, driving directions, location based business searching and traffic information services.
Additional geocoding-related API's:

Yahoo Geocoding API

Map24 API

ArcWeb Services JavaScript API

Harvest provides two API interfaces: one for Timetracking and another to access and edit your projects, clients, users and tasks through the Extended REST API.
Additional project management-related API's:

Basecamp API

Unfuddle API

iStockphoto provides web services via an XML-RPC API. The web service provides access to a wide range of iStockphoto.com functionality and content including: full search capabilities, lightbox management, file downloading, member statistics, contributor portfolio management, and image uploading.
Additional photo-related API's:

Windows Live Spaces Photo API

AOL Pictures JSON API

GIMP API

The MapQuest® Developer Network is the one-stop resource for all MapQuest APIs, related documentation, sample code, and articles.
Additional map-related API's:

Google Static Maps

OpenStreet Map API

MetaCarta GeoParser API

The Google Contacts Data API allows client applications to view and update Contacts content in the form of Google Data API feeds. Your client application can request a list of a user's contacts, edit or delete content in an existing contact, and query the content in an existing contact.
Additional contacts-related API's:

Plaxo Address Book Access Widget

Apex (Salesforce.com) API

Wakoopa API

The API returns Twitxr data in a form that can be easily integrated into any application or web site. With Twitxr you can share a moment, a picture, a thought, instantly with your mobile phone. Automatically post to your Twitter, Flickr and Facebook profile.
Additional picture-related API's:

Flickr API

Facebook API

Twitter API