If the idea of exploring through a list of third-party APIs that are publically available excites you to build a new app, then the following list of API Directories is for you.

The oldest and most well known place for APIs and mashups. As of writing this article, Programmable Web lists 11,000+ APIs and 7000+ Mashups. Together with the Programmable Web Blog, they keep you up-to-date with the latest API additions, most popular APIs and other insights and strategies.

You can easily filter their API directory by Category, Company, Protocol, Data Format or Keywords.

APIS.io is an open source and free API registry service that allows developers to publish and discover REST APIs and interact with them online. They provide:

API Directory of REST APIs allowing developers to discover, document, and interact with APIs and list mashups using them.

of REST APIs allowing developers to discover, document, and interact with APIs and list mashups using them. API Explorer for interacting with REST APIs. Saving requests and responses to share with other developers.

for interacting with REST APIs. Saving requests and responses to share with other developers. API Configurator that allows you to import and export WADL definitions as well as create APIs through realt-ime user interface.

Public APIs is an API listing created by Mashape. It lists more than 10,000 APIs.

The Mashery API Network allows you to register once and gain access to 40+ Mashery-powered APIs with a single sign-on. Get hands on quickly using their API Explorer or get inspired by browsing through the App Showcase.

Exicon simplifies the creation and management of apps for some of the world’s biggest companies. You can search, discover, benchmark, distribute and promote APIs and mobile apps through their directories.

theRightAPI is an online tool to discover, trust, monitor and manage APIs. theRightAPI also helps you by allowing you to define any API scenario to see exactly how it behaves now and at any point in the future.

Did we miss out on any of your favorite API directories? Let us know in comments.