There are two aspects to a butterfly garden:
1. Attracting adults to feed
Some species of butterfly also drink sap exuding from trees and the juices of rotting fruit. Try leaving cut fruit on a bird table in your garden.
2. Attracting adults to breed
Often older leaves of plants contain more toxins than young leaves, so it is a good idea to prune regularly any bushes or trees that you grow in order to encourage new growth.
Some specific plants for butterflies that have adapted to suburban gardens in Australia are:
For other species, there is a problem. Plants and butterflies have co-evolved over the last 100 million years with plants producing poisons and butterflies producing antidotes. So there has been divergent evolution ending up with many families of plants each with different poisons, and many butterfly species each being able to metabolise the poisons of one plant family. So to attract many species of butterflies to breed you will need plants from many different families, see list at:
Further reading :
Butterflies and Other Invertebrates Club
Gardening for Butterflies.
Flowers in Australia
(updated 29 November 2009)