As of February 9th, 2019 we are now listed on https://www.programmableweb.com/
ProgrammableWeb is more than just an API Directory service, it’s an informational resource for APIs: Stuff like whether they use XML or JSON, do they have spec docs? Versions, endpoint information, SOAP or REST and other ecosystem related queries one might have. They also have a very interesting blog for people who wish to watch the scene.
If you want to learn more about APIs, you should really check out David Berlind’s APIs 101 series on youtube.