Here are some of the Web API's that I want to experiment with more:
- Yahoo PHP Developer Network
- Google SOAP Search API
- ebay PHP developers page
- Amazon E-Commerce Services
- flickr the photo sharing site API
- Yahoo Maps
- Bloglines API
- Backpack API (I have not used this site - but it looks cool
- del.icio.us
- English Stantard Version Bible as a Web Service
- Alexa developer's corner
- upcoming.org api
