Editors & IDEs
Rails is blessed with multiple startups dedicated to helping you track and improve the performance of your applications: New Relic and Scout. Any high traffic Rails application should use one of these.
While Rails hosting is now common place, there's a handful of dedicated Rails hosting companies that have been around for a long time and supporting the community: Rails Machine, Joyent, Brightbox, Engine Yard, and Heroku. If you're just looking for a VPS, we recommend Rackspace (who've gracefully donated machines to run some of our infrastructure) or Linode.
Lots of Rails consultants stand ready to help develop your application or train your team. Koz from core works individually and both WyeWorks and Plataformatec are led by core members. We also like the teams from entp, thoughtbot, Pivotal Labs, Fingertips, Planet Argon and Phusion. You can find even more consultants at Working with Rails.