Check out this article for some big outdoor toy ideas.
I remember my older brother rigging up a slip 'n slide for us when I was little with garbage bags and sprinklers. And then when my mom saw the lovely garbage bag display across the backyard, she promptly bought us a real one that looked more, well, presentable! LOL

http://today.msnbc.msn.com/id/25373328/

I was one of those who thought all the big ole yard toys looked so tacky. That was before my LO came along and he loves being outside and gets bored quickly. Yes I still think they look tacky but I now have some in our yard.
I am at a loss as to why I feel the need to get my LO these things (oh he should have a sandbox, he should have a swingset, he should have a pool with a slide, wagon, trike, dump truck, etc.....). I had none of these growing up. At best I had a hand-me-down basketball and an old rusty ring with no net nailed to a tree. I invented my play. If I seemed bored my Mom always found some work that needed to be done lol. I managed to have fun though and remember many good times. I don't think I was slighted in any way by not having a Little Tikes cottage or a 10 ft. Bonzai slide. I hope I can learn to balance giving my LO the moon and having him learn to create it.