Updated Feb-2015
Codeship
There was a lack of development on Drone.io so I switched to Codeship and I'm thoroughly enjoying it. It's actively developed and improved, has great design and is very fast. Plus, for the bottom tier it's actually free (up to 100 builds per month) so it ended up being cheaper than Drone.io.
Original Answer
Drone.io
I just setup our main Ruby on Rails application with http://drone.io/. Was a piece of cake and it's got a great interface. I'd say worth checking out if you're looking for a simple, hosted solution.
