Toni,~~Nice spotlight on one of the most popular garden plants to attract a very long list of butterflies for nectaring including Monarchs, Swallowtails, Fritillaries, Red-spotted purples and many others.
One drawback to planting buddliea, though, is the invasiveness that you mentioned (a number of states have 'outlawed' it or strongly discourage its planting). I just wanted to point out that hybridizers are working on developing sterile versions that will reduce the risk of invasiveness to make a viable choice for many gardeners, especially those in warm climates.
The well-known Plants Delights Nursery people wrote an informative article about the range of Buddlieas available in todays market, including some examples of less invasive varieties. Here is an excerpt:
"For gardeners whose property borders a non-forested natural area, use the sterile or low fertility cultivars or remove the seed heads in the fall before they open. Many of the modern cultivars of Buddleia davidii have dramatically reduced fertility and are not invasive. Some hybrid cultivars (such as 'Blue Chip') are almost completely sterile and pose no threat. Some low viability selections include Buddleia weyeriana, Buddleia fallowiana, Buddleia hemsleyana, Buddleia longifolia, Buddleia macrostachya, and Buddleia nivea."
Another interesting point is that there are buddlieas other than the ubiquitous B. davidii that are considered native to our southeast.