The Surge Gyms NOR offer excellent group fitness classes; such a great selection and also a great crèche. I'm also a fan of the community leisure centres at Joondalup arena, Craigie Leisure Centre and Wanneroo. Great gyms and with easy casual payment options for when you don't want to fork out for a gym membership.
Lords in Subiaco is far and away the most comprehensively equipped gym in Perth. The weights area is huge, and the complex itself has everything: gym, cardio equipment, boxing equipment, tennis courts, a pool, spin bikes and fitness classes.