SQL Azure - Microsoft Azure Cloud SQL Database is the developer’s cloud database service. The Azure database as a service is your solution to building and monitoring applications quickly and efficiently.
MySQL - The world's most popular open source database
Database.com - Enterprise cloud database
PostgreSQL - PostgreSQL is a powerful, open source object-relational database system.
Heroku Postgres - Heroku Postgres is an SQL database as a service.
SQLite - SQLite Home Page