How to stop an Oracle AQ queue

Run the following as an anonymous block of PL/SQL:

BEGIN
DBMS_AQADM.STOP_QUEUE(queue_name => 'my_queue_name', enqueue => false, dequeue => true);
END;

The above stops dequeuing from the queue (because dequeue=true).
The opposite command is START_QUEUE.

Useful post on working with AQ:
http://www.oracle-developer.net/display.php?id=411

And if you're looking for how to view the data that's on your queue, see this page:
http://rwijk.blogspot.com/2009/02/whats-in-my-jms-queue.html
Very useful post on how to look into the data, e.g.
SELECT QT.USER_DATA.TEXT_VC FROM <queue table name> QT;
(note use of QT table alias to refer to it...)