Bottle bottom turtles - too cute! Just need a turtle shape and the bottom of a bottle! (for a big turtle) or you can use smaller bottles for smaller turtles. Make it fun and let the kids decorate their turtles with glitter and stickers too!
DIY hanging planters - (the link is for purchasing) - this is easily a DIY project - made with two liter soda bottles painted and holes punctured and threaded with fishing line, or even jump rings through the holes and decorative chain to hang with.
How to Recycle Plastic Bottles for Bird Feeders, Creative Ideas for Recycled Crafts
How to make a Sub-Irrigated Planter. I'm not sure I would use a two liter plastic bottle though. Over time I would fear the plastic breaking down enough to poison the plant. Perhaps a wine bottle instead.
2 Liter Bottles of Light provide as much light as a 50 watt light globe. The slums of the Philippines are getting an extreme home makeover in the form of two liter bottles in their ceilings. The bottles function as lights powered by solar energy.