List Concatination

Folks,
I have an interesting problem.  For purpose of presentation to users,
I'd like to concatinate a list of VARCHAR values from a subtable.  To
simplify my actual situation:

CREATE TABLE clients (client_id SERIAL PRIMARY KEY,client_name VARCHAR(50) );

CREATE TABLE client_contacts (contact_id SERIAL PRIMARY KEY,client_id REFERENCES clients(client_id),first_name
VARCHAR(25),last_nameVARCHAR(25) );
 

CLients:
1     McMurphy Assoc.
2    Ross Construction

Contacts
1    1    Jim    Henson
2    1    Pat    O'Gannet
3    2    Sara    Vaugn
3    2    Bill    Murray

etc.

What I'd like to be able to do is present a list of clients and their
comma-seperated contacts in paragraph form, hence:


Client            Contacts
McMurphy Assoc.        Jim Henson, Pat O'Gannet, Kelley Moore

Ross Construction    Sara Vaugn, Bill Murray, Peter Frump,        Siskel Ebert

I can figure out how to do this procedurally (using PL/pgSQL and a
cursor) but not how to do it declaratively (using only SQL).  The reason
it's important to do it declaritively is that there are actually two
sub-tables with thousands of entries and the procedural approach is
rather slow.

Suggestions?
                    -Josh Berkus

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