The pgadmin3 GUI client for PostgreSQL is terrible.
The other choice is the web client phpPgAdmin.

Install

sudo apt-get install phpagadmin

This will install a conf file for apache at /etc/apache2/conf.d/phppgadmin, and restart apache.

Fix apache conf

However, when you visit url http://localhost/phppgadmin/, it doesn't work.

The problem is, in the latest version of /etc/apache2/apache2.conf, it doesn't load conf files in conf.d at all. But it has these lines:

...
# Include the virtual host configurations:
IncludeOptional sites-enabled/*.conf
...

That means it will load .conf files in sites-enabled. So we can do:

sudo ln -s /etc/apache2/conf.d/phppgadmin /etc/apache2/sites-enabled/phppgadmin.conf
sudo service apache2 restart

Now, if you go to http://localhost/phppgadmin/, it works now. Congratulations!

Fix security conf

But hang on, when I try to login with postgres/PASSWORD (need to set password first, refer to my last post), it fails with a message on top:

Login disallowed for security reasons.

Then in /etc/phppgadmin/config.inc.php, I find this:

// If extra login security is true, then logins via phpPgAdmin with no
// password or certain usernames (pgsql, postgres, root, administrator)
// will be denied. Only set this false once you have read the FAQ and
// understand how to change PostgreSQL's pg_hba.conf to enable
// passworded local connections.
$conf['extra_login_security'] = true;

Since I am using it on localhost, so security doesn't matter here. Change true to false, and restart apache:

sudo service apache2 restart

Now, go to http://localhost/phppgadmin/ and login, it will work. Enjoy :-)