PostgreSQL

PostgreSQL is a SQL database product. It is comparable to MySQL.

PostgreSQL is the platform for PostGIS, a set of GIS extensions for handling geospatial data.

As of November 2010, Dreamhost does not support PostgreSQL. There is a Suggestion open on the Dreamhost Control Panel to add support. Go there and vote if you'd like to see it added.

PostgreSQL on DreamHost PS
There is a post on the DreamHost discussion board about installing PostgreSQL on DreamHost PS. See the Dreamhost discussion board for more information.