This list has been superseded by Public APIs. Check there for APIs with Auth: No, HTTPS and CORS Yes.
List of data APIs that require no server-side auth or private credentials, and are thus good for small browser-only JS projects.
- 3taps (information)
- Adobe Creative SDK (image editing)
- App.net
- Bing Maps
- Echo Nest (music)
- Etsy (shopping)
- Facebook Graph API (JS SDK allows auth via client-side)
- Flickr (images)
- Foursquare (location)
- Gilt (shopping)
- GitHub (code)
- Google
- Google Knowledge Graph (information)
- Google Maps
- Google Plus (people)
- Youtube
- Gravatar
- Grooveshark (music)
- HERE (maps)
- Instagram (images)
- Lob (mailing address verification)
- Mapbox (maps)
- Mapzen plugins and data (maps)
- Markit On Demand (stocks)
- Meetup
- Metropolitan Museum of Art
- OpenStreetMap (maps)
- OpenTok (videochat)
- Pearson (publications)
- SoundCloud (music/audio)
- SpaceAPI (hackerspace directory)
- Spotify (music)
- Stripe (payment)
- Transitland (public transit)
- Tumblr
- Twilio Client (audio/video)
- Vimeo Simple API (video)
- Wikipedia, via DBpedia or MediaWiki (information)
- Wolfram Alpha (information, math, etc.)
OpenUV - Global UV Index Forecast API for Sun Safety information: https://www.openuv.io