Short.io - Short.io makes short links (vanity urls) on your own domain. Free signup, analytics and API. Chrome, slack, zapier and segment integrations.
Shorten.REST - A URL shortener API you can depend on
Cutt.ly - Free custom URL Shortener and branded URLs with advanced links tracking and Link Management Platform & API.
PixelMe - URL shortener for savvy marketers
my.new - Create shortened URLs that do stuff
Pixela - Record and Track your habits or effort. All by API.