We have

cubbby house with climbing stuff, swing, slide
sand pit
swing set
trampoline
pool
bikes, trikes, scooters
bouncy castle (don't have it up all the time though)
toy box full of stuff like balls, frisbees, mini golf, soccer nets, sidewalk chalk, finger painting, bubbles etc

In our last house where we had a much smaller backyard we had a tiny blow up pool for the kids and one of their favourite things was a little plastic slide going into it. They sort of rebound off the soft edge of the paddle pool and had an absolute ball.