A butterfly garden is a great way to attract butterflies to your yard because it provides flowers that they like to feed and lay eggs on. A butterfly garden can be any size... while it's great to have a plot of land to use, a "windowbox" butterfly garden is also a great idea if you have limited space1!
Here are some cool sites with descriptions of how to plant a butterfly garden of your very own:
References:
1) (2009). Butterfly gardening. Retrieved April 11, 2009, from The Butterfly Site Web site: http://www.thebutterflysite.com/gardening.shtml