determine sequence name for a serial

I am trying to track down a method of determining what a sequence name
is for a SERIAL is in postgresql.

For example,

CREATE TABLE foo (id SERIAL PRIMARY KEY NOT NULL, bar TEXT);

\d foo
                           Table "public.foo"
 Column |  Type   |                      Modifiers
--------+---------+-----------------------------------------------------
 id     | integer | not null default nextval('public.foo_id_seq'::text)
 bar    | text    |
Indexes:
    "foo_pkey" primary key, btree (id)

Now, I have figured out how to get a list of all the sequences with:

foo=> SELECT relname FROM pg_class WHERE relkind='S' AND relname !~ '^pg_';
  relname
------------
 foo_id_seq
(1 row)

I can find public.foo in pg_tables, but I am not sure how to relate pg_tables and pg_class in order to find the
sequencefor a specific field in public.foo. 

Can anyone point me in the right direction? I am trying to get out of the habit of hard-coding the sequence names in my
code. 

Now that I think of it, I am lacking 'public.' as well from my query.

Ok, so how would I go about getting the sequence name for a SERIAL field on any given schema.table? I would like to
builda function that would return this value if I pass it the schema and table (and fieldname is necessary) 

Thanks,

Robby


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