Nearly all the standard data modelling tools(ERwin,System Architect, Enterprise Architect ...) have a facility for reverse engineering a schema. This produces an ER diagram for the schema. It's worth pointing out however that this diagram gives you structure not semantics. The latter has to come from elsewhere.

Not an E/R diagram, but to generate table diagrams that you can navigate (in HTML), SchemaSpy (http://schemaspy.sourceforge.net/) is really good.

I use DBSchema for ER diagrams, works well. http://www.dbschema.com/screenshots.html

We use lucidchart and balsamiq at times to model ERDs using the crow's foot style. There are certain gems for Ruby on Rails dev that generate ERDs from the schema,.

LucidCharts has a decent import feature for a PostgreSQL schema.