We've said it before, and we will say it again: If you want to attract birds to your yard, you need to offer a water source. And this isn't just a suggestion, according to Cornell University, it is one of the best things you can do for your fine feathered friends.
However, not all bird baths are created equal. There are some do's and don'ts as well as some guidelines that will help yours be the most attractive:
DO NOT add glycerin or antifreeze to a bird bath. This has become somewhat common among birders because it keeps water from freezing in the winter. However, antifreeze is poisonous and glycerin can matt the feathers.
DO use a heated bird bath or de-icer during cold months. These are specifically designed to prevent the bird bath from entirely freezing over and keeping the water above freezing. It is not necessary to heat the water more than that.
DO include a water wiggler, dripper or sprayer for your bird bath. Not only will the moving water be much more attractive to the birds, but it will also help slow algae growth and prevent mosquitoes from laying eggs. However...
DO NOT use a water wigger, dripper or sprayer as a substitute for cleaning your bird bath. Birds will still leave feathers and droppings in and around the bath, and water can get very unsanitary very quickly. Empty the birdbath every few days (immediately, if you see algae forming), clean and refill with fresh water. Clean or replace anything you have in the bath as well.
The best baths mimic what birds use in nature: puddles and other shallow waters. While the stone or glass pedestal baths are pretty, low profile, easy to clean baths in shady area will be more attractive to the birds. You will also want to find bird baths that are less than 2 inches deep. Adding stones and twigs to your bath will give birds a place to perch and preen.
For further reading, check out this PDF from Cornell University's Lab or Ornithology.