function to return rows as columns?

Hello,
    i have a query that returns a result set like this:

item | size | stock
123  | XL   | 10
123  | XXL | 5
123  | XS   | 3

and i would like get the results like this:

item | XL | XXL | XS
123  | 10  | 5     | 3

i have been thinking how to do it with a plpgsql function but the number of
sizes depend on the item that it is queried so i can not create a type and
return it, i could create it like a text concatenating the stock and size of
every row and returning the complete line text but i would have to process it in
the application anyway so i am searching a solution that lets me return it like
a record.

I have been searching the list and maybe i could create the record type inside
the function and to get the correct names and number of columns in the
application side launching a query to get the number of sizes before call the
function to specify the columns in the function call but maybe i am missing
anything important here? any better (or more correct) way to do this? Thanks.

Regards,
Miguel Angel.