Hey Aidan! I'm glad to see you're still helping newbs like me.

http://www.tokbox.com/opentok/api/features Opentok API for a videochat application.

I'll update this as I remember more.

http://hunch.com/developers/v1/

https://dev.gilt.com/page/gilt-public-apis

http://api.mongodb.org/

http://www.meetup.com/api

I really like Kinetic.js for html5 games and animations. The concepts are based on flash and its very user friendly to start. http://www.html5canvastutorials.com/kineticjs/html5-canvas-drag-and-drop-the-stage-with-kineticjs/

@softprops the docs make exposing the API key sound scary... does it just identify the user, or actually allow the API to make changes on behalf of them? (I would hope the former)

@pencilking2002 sure, tons of good JS libraries for widgets, drawing, animation, etc. - I just meant REST APIs for getting 3rd-party data

twilio

Etsy has a nicely documented JSONP api: http://www.etsy.com/developers/documentation/getting_started/jsonp

Balanced isn't read-only, but it's a REST API sans OAuth:
https://github.com/balanced/balanced-api

http://webshell.io/ looks a bit promising too. It's... sort of like an API for APIs. but allowing for easy mashing up.

http://www.html5video.org - https://github.com/kaltura/mwEmbed

You can use Aviary to edit any photo with a public url (from tumblr, foursquare, facebook, flickr, etc). On save, it spits back out a url to the saved image which you can publish back to the platform.

twilio++

Would love to see some SendGrid action on here too.

We have a number of no-auth endpoints at App.net (anything that has Token:None on this list http://developers.app.net/docs/resources/ )

http://scrAPI.org has metropolitan museum of art data, all from their website :)