Here are Top 10 APIs for beginners

1. Dropbox: https://www.dropbox.com/developers
2. Google Maps: https://developers.google.com/maps/web/
3. Twitter: https://dev.twitter.com/docs
4. YouTube: https://developers.google.com/youtube/v3/getting-started
5. Soundcloud: http://developers.soundcloud.com/docs/api/guide#playing
6. Stripe: https://stripe.com/docs/tutorials/checkout
7. Instagram: http://instagram.com/developer/
8. Twilio: https://www.twilio.com/docs
9. Yelp: http://www.yelp.com/developers/getting_started
10. Facebook: https://developers.facebook.com/docs/facebook-login/login-flow-for-web