List of data APIs that require **no server-side auth or private credentials**, and are thus good for small browser-only JS projects.

* [3taps](http://3taps.com/developers-overview.php)
* [Aviary](http://www.aviary.com/web)
* [Bing Maps](http://msdn.microsoft.com/en-us/library/dd877180.aspx)
* [Echo Nest](http://developer.echonest.com/)
* [Etsy](http://www.etsy.com/developers/documentation/getting_started/jsonp)
* [Facebook Graph API](https://developers.facebook.com/docs/reference/api/)
  - [JS SDK](https://developers.facebook.com/docs/reference/javascript/) allows auth via client-side
* [Flickr](http://www.flickr.com/services/api/)
* [Foursquare](https://developer.foursquare.com)
* [Freebase](http://wiki.freebase.com/wiki/Freebase_API)
* [Gilt](https://dev.gilt.com/page/gilt-public-apis)
* [Github](http://developer.github.com/)
* Google
  - [Google Maps](https://developers.google.com/maps/documentation/javascript/tutorial)
  - [Google Plus](https://developers.google.com/+/api/)
  - [Youtube](https://developers.google.com/youtube/)
* [Gravatar](http://en.gravatar.com/site/implement/)
* [Grooveshark](http://developers.grooveshark.com/)
* [HERE](http://developer.here.net/) (Nokia maps)
* [Hunch](http://hunch.com/developers/v1/)
* [Instagram](http://instagram.com/developer/)
* [Meetup](http://www.meetup.com/meetup_api/)
* [OpenTok](http://www.tokbox.com/opentok/api/features)
* [Pearson](http://developer.pearson.com/apis)
* [Reddit](http://www.reddit.com/dev/api)
* [SoundCloud](http://developers.soundcloud.com/)
* [Spotify](https://developer.spotify.com/)
* [Stripe](https://stripe.com/docs/stripe.js)
* [Tumblr](http://www.tumblr.com/docs/en/api/v2)
* [Twilio Client](http://www.twilio.com/client)
* [Twitter REST API](https://dev.twitter.com/docs/api/1.1)
* [Vimeo Simple API](http://developer.vimeo.com/apis/simple)
* Wikipedia
  - [DBpedia](http://dbpedia.org/About) 
  - [MediaWiki](http://www.mediawiki.org/wiki/API)
* [Wolfram Alpha](http://products.wolframalpha.com/api/)

See also:
* [Apigee App Services](http://apigee.com/docs/app_services)
* [jsonp.jit.su](http://jsonp.jit.su/)
* [popular APIs on ProgrammableWeb](http://www.programmableweb.com/apis/directory/1?sort=mashups)
* [Webshell](http://webshell.io/)