I think this is so cool! Check out how buried unglazed clay pots make a very effective watering system for your plants in the garden.
You can find a bunch of info here at Tipnut. There is also a few other neat ideas Tipnut shares using other items like coke bottles, buckets etc. Here is a great example as to how to use clay pot ollas in a raised garden bed at website called A Path to Freedom. This website has a lot of good ideas about edible landscaping too. Some of their ideas are little extreme for me, but their story is really interesting I think :-) They turned their yard in the middle of the city in Pasadena CA. into a thriving organic gardening business. They sale a lot of fruits and veggies to local resturants etc.