Dbvisualizer (http://www.dbvis.com/) works with lots of databases and is really pretty cheap. Disclaimer: no connection other being a long term customer, I use it with Oracle, MySQL and Postgresql.

Try pgAdmin at http://www.pgadmin.org/

Edit: You can also check phppgadmin at http://phppgadmin.sourceforge.net/doku.php

TeamPostgreSQL is a very good web GUI for PostgreSQL: http://www.teampostgresql.com

Check out Navicat and you will never touch phpMyAdmin again.