CloudSight - Image recognition API; send an HTTP request with an image, get a description of contents.
Momixa - Pick two songs and get the perfect mix
Flico - Add visual search to your Chrome browser
Music Suggestions Ninja - Enter an artist's name & find similar, lesser known artists
Google Vision AI - Cloud Vision API provides a comprehensive set of capabilities including object detection, ocr, explicit content, face, logo, and landmark detection.
Boil the Frog - Create a seamless playlist between any two artists