PLPGSQL func. defn. for returning resultset?

Hello,

I need to write some functions/stored procedures in PLPGSQL.
All examples have a return clause that returns a single item (e.g. 
RETURN INTEGER or RETURN VARCHAR, etc.).

However, I need to return a result set (e.g. SELECT user_id, name FROM 
users).  What do I specify in the return part of the FUNCTION definition 
for that?
CREATE FUNCTION foo() RETURNS ????? AS ' .....
What do I put in place of ?????

I could not find any examples for such cases.

Thanks,
Otis