SELECTing the last value inserted into a SERIAL column

I have a table(a) where I want to use a unique number as the primary key. I had intended on using the data type SERIAL to do this, and letting the system merely increment it for each INSERT into table(a). However, I want to be able to capture the SERIAL value that was just inserted into table(a) so I can insert the value into another table(b). This would happen in the same transaction as the INSERT into table(a). Is there a way to retrieve the SERIAL value that was just INSERTed into table(a)? Or would I be better off using a nextkey table to hold the next value of the key to be inserted, and basically doing the job of the SERIAL data type manually? Thanks. -Clay Amerault