I'm looking to deploy a Rack based app on Heroku and I have been checking out different database solutions. Amongst MongoHQ, MongoLab, Heroku DB hosting, Amazon RDS, and Xeround, the MongoDB solutions are significantly cheaper than the SQL solutions. I know price should not determine which DB you use for your app but the price differential is significant.

Check out the prices: - Amazon RDS: http://aws.amazon.com/rds/pricing/ - Xeround: http://xeround.com/pay-per-use-cloud-database/ - Heroku: http://www.heroku.com/pricing#0-0 (Scroll down to the database options) - MongoHQ: https://mongohq.com/pricing - MongoLab: https://mongolab.com/about/pricing/