If you go to the lower league games
Wests(mind you West hate everyone) vs Balmain they hate each other
Illawarra vs St George (in the juniors have had games where Craig Young has had to go onto the field and tell both sets of teams to settle down)

When I was at the Bears and we made the Premier League Grand Final in 07, it was amazing to see how many people had a soft spot for Norths with people often referring to them as their "second favourite team"