You could check out Ruby on Rails Hosting, What is a good Ruby on Rails hosting service?, Good Ruby on Rails free hosting, and What is a good Ruby on Rails and PHP hosting?.
I personally prefer Heroku which has offers free low-scale hosting and is very easily upgraded. Also, they allow you to install gems (similarly to the gem dependencies and rake gems:install, but with different syntax/files), and send a few free emails (200, but it is easily upgraded).
