Finding all tables without PK (Primary Key) or indexes on PostgreSQL

tables-without-indexes.sql

SELECT 
	c.table_schema,
	c.table_name,
	c.table_type
FROM 
	information_schema.tables c
WHERE  
	c.table_schema NOT IN('information_schema', 'pg_catalog') AND c.table_type = 'BASE TABLE' 
  AND NOT EXISTS(SELECT i.tablename  
				FROM pg_catalog.pg_indexes i 
			WHERE i.schemaname = c.table_schema 
				AND i.tablename = c.table_name AND indexdef LIKE '%UNIQUE%')
  AND
NOT EXISTS (SELECT cu.table_name 
				FROM information_schema.key_column_usage cu
				WHERE cu.table_schema = c.table_schema AND
					cu.table_name = c.table_name)
ORDER BY 
	c.table_schema, c.table_name;

tables-without-pks.sql

SELECT
    n.nspname AS "Schema",
    c.relname AS "Table Name",
    c.relhaspkey AS "Has PK"
FROM
    pg_catalog.pg_class c
JOIN
    pg_namespace n
ON (
        c.relnamespace = n.oid
    AND n.nspname NOT IN ('information_schema', 'pg_catalog')
    AND c.relkind='r'
)
WHERE 
    c.relhaspkey = false  
ORDER BY 
    c.relhaspkey, c.relname
;

More information,
http://www.postgresonline.com/journal/archives/65-How-to-determine-which-tables-are-missing-indexes.html