I've seen those cool aqua globes, but can't get my fugal self to spend money on them. Last year I tried the wine bottle in the potted plant while i'm on vacation trick.
It worked fairly well while we were gone on a weeks vacation. But I'm sure my neighbors were wondering how much wine I really drink....
This year I decided to tweak the idea just a bit. If you can invert the bottle and water over a long time I thought why not punch holes in the bottom of a 2 liter bottle and bury it in the pot, then fill it with water and let it soak up from the bottom. It will serve the purpose of watering my plants while on vacation, give them a source of extra water on really hot days, and I don't look like an alcoholic or pop addict with bottles sticking out of my plants while i'm gone.
Step one: cut several holes into the bottom of a 2 liter bottle. Coke has those neat little feet that you can cut off. (I also added a few small slits randomly on the lower half if the bottle) Be careful, a sharp strong kitchen shears and some firm plastic will make for a slippery surface. (as you can see by the Mickey Mouse bandaid on my hand)
Step two: add a small layer of soil on the bottom so the top of the bottle will be just above soil level once the pot is full.
Step three: fill with potting soil. Add plants. Water. Enjoy the beauty of nature!