At times I feel like a snob for admitting it, but plastic things really upset my sense of beauty. I can tolerate it in the house at times (yes, I do own Tupperware!) but when it comes to plastic outside, the contrast between the artificialness of plastic riding toys, swingsets, etc. and the vibrancy and realness of the natural world is jarring. So whenever I can, I try to find ways to eliminate outdoor plastic fixtures.
I find that for babies, a galvanized metal tub makes a fun wading pool. While it's not really big enough to swim it, it definitely takes the edge off the last hot days of summer. And even bigger kids like to soak in it. I've found that one of these tubs (we just "upgraded" from a 30 gallon to a 45 gallon model this summer - $25 at the hardware store) and a good sprinkler is all the water fun my small children need.
And this fall, we can use it for bobbing for apples. :)