A beautiful DIY with plastic bottles. Tip: Use a medium hot iron and place it on the mouth of the bottle to connect the finish! Use baking paper between the Iron and the bottle, so you don't ruin the iron!
The Chic Technique: Plastic Cup Sun Catcher Mobile by Erin Barnes This is made out of recycled plastic cups. Shrunk like shrinky dink plastic and hung so beautifully into this mobile/sun catcher. What a great older kid project as well.
DIY Plastic Bottle Recycling: Starting/Planting garden plants in milk jugs; Most Intriguing -- the milk jug igloo -- on a raised base with the entrance on the leeward side, this could be a nice place to play even in cooler weather.