List the database privileges using psql

postgres=> \l
                                  List of databases
   Name    |  Owner   | Encoding |   Collate   |    Ctype    |   Access privileges   
-----------+----------+----------+-------------+-------------+-----------------------
 postgres  | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | 
 template0 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +
           |          |          |             |             | postgres=CTc/postgres
 template1 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +
           |          |          |             |             | postgres=CTc/postgres

The docs on Privileges give an explanation of how to interpret the output. For specific privileges on a table of the current database, use \z myTable.

perhaps you mean listing users and their privileges for a database - I can't quite tell from the question:

postgres=> \du
                             List of roles
    Role name    |  Attributes  |                    Member of
-----------------+--------------+------------------------------------------------
 dba             | Create role  | {util_user,helpdesk_user,helpdesk_admin}
 helpdesk_admin  | Cannot login | {helpdesk_user}
 helpdesk_user   | Cannot login | {helpdesk_reader}
 jack            |              | {helpdesk_admin}
 postgres        | Superuser    | {}
                 : Create role
                 : Create DB

You can do that by following:

SELECT grantee, privilege_type 
FROM information_schema.role_table_grants 
WHERE table_name='mytable'

This gives you this kind of output:

mail=# select grantee, privilege_type from information_schema.role_table_grants where table_name='aliases';
   grantee    |  privilege_type
--------------+-----------------
 mailreader   |  INSERT
 mailreader   |  SELECT
 mailreader   |  UPDATE
 mailreader   |  DELETE
 mailreader   |  TRUNCATE
 mailreader   |  REFERENCES
 mailreader   |  TRIGGER
(7 rows)

mail=#