https://semaphoreci.com/:

• $30/month for 1 box
• $99 for 2 boxes + docker support
• free for open source and 100 private builds
• looks well designed
• ubuntu 14.04 for build machines

https://codeship.com/:

• $0, 1 concurrent build, 1 parallel test, limit 100 builds
• $49 1 concurrent build, 2 paralles test
• $99 2 concurrent builds, 2 parallel test
• docker support: add $75

https://circleci.com/:

• $0, 1 container, 1 concurrent build, limit to 25 hrs of build time
• add $50 for additional container

https://travis-ci.org/:

• free for open source
• $69 1 concurent job
• $129 2 concurrent jobs
• has osx builds
• ubuntu 12.04 for container, ubuntu 12.04 or 14.04 for full vm

https://drone.io/:

• free for public projects
• $25 for 5 private projects
• $49 for unlimited private projects
• also self-hostd version

http://www.wercker.com/

• free for 2 concurrent jobs
• $350 for unlimited

https://www.appveyor.com/

• windows support
• $29/month, 1 private project
• $59/month, unlimited projects, 1 concurrent
• $99/month, unlimited projects, 2 concurrent
• free for open-source