Thanks to suggestions from readers over the past 24 hours, I've added four more APIs to the list:
- Syndic8: An excellent directory of syndicated news headlines with a rich XML-RPC API (since 2001 no less).
- smugmug: online photo sharing service with XML-RPC and REST APIs along with dedicated hacks page on their site.
- voo2do: interesting task management service ala Joel Spolsky's model.
- Digital Podcast: new podcast search service via REST API.