SELECT  proname
FROM    pg_catalog.pg_namespace n
JOIN    pg_catalog.pg_proc p
ON      pronamespace = n.oid
WHERE   nspname = 'public';

With thanks to Quassnoi from http://stackoverflow.com/questions/1559008/list-stored-functions-using-a-table-in-postgresql
If you are using psql client you can simply type:
\df

And to view the stored procedure code:
\df+ procname