In Australia, CASA says we are to have a minimum of 4 crew on a B737/A320. Jetstar and Virgin Blue went from having 5 on their aircraft down to 4 when CASA granted the reduction some time last year (I think).
However, at Jetstar we've recently gone back to 5 crew as standard ops on the A320, I think due to the lack of crew rest breaks being achieved with reduced crew (4).
The A321 which has just entered service with JQ will be crewed by 6. We have one crew member at each of the full-size exits L1, R1, L4 and R4, and then we have one stationed at Doors 2 who will command the ABPs at L2/R2 to either open or block the exit, and another crew member at Doors 3 who will instruct ABPs at L3/R3.