Well Tom, I have noticed in the past that there seem to be different regional nectar plant preferences even within the same butterfly species. If you really want the Swallowtails, I would say to plant host plants for them. If you have a spot for it, some Pipevine would be great. Some Fennel, Dill, or Parsley would be good. One of my Florida friends is having great success with his Prickly Ash. (Toothache Tree) Wafer Ash (Hoptree) is wonderful. And for nectar sources, I think that you can't have too much Lantana. Zinnias are wonderful too.
Angie

Check here for butterfly host plants:
http://faq.gardenweb.com/faq/lists/butterfly/2004041551026161.html

How about some pipevine or spicebush?

Gotta hunt down something called Cestrum diurnum...
How far are you from the coast? You might try growing some Coontie (Zamia floridana, pumula) in a shady spot if you are near enough to the coast to attract the Atala, an endangered and gorgeous butterfly.
Passiflora suberosa will attract Zebra Longwings and the Julia, as well as the Gulf Frittilary.
Any Cassia is essential for Sulfurs.
Wild Lime is a Florida native that attracts Giant Swallowtails.
Whitevine attracts Queens, Monarchs and Tropic Queens.
Some good nectar sources are Firebush (Hemelia patens) and Jatropha multifida (Red Coral Tree)
Can't go wrong c Mexican Sunflower (Tithonia).

Did I mention Porter Weed as an excellent nectar source? It comes in blue, white, purple and salmon pink. All attract butterflies, bees and hummers.

Thanks for all the great ideas....gives me some weekend research to do!

I vote for spicebush, and sassafras as well!

Here is a link that might be useful: Sassafras

Oh, don't forget green shrimp, and or ruellia, for Malachites. Pawpaw, for zebra swallowtail. I raised 15 this year on mine. And I highly suggest wafer ash for Giant swallowtail. No thorns.

I don't believe that Sassafras does well that far south.

Do some research on host plants for Zebra Swallowtails. There is another plant that does well in your growing area other than paw paws--which take a long time to grow.

You have some excellent suggestions above.

Check out a small tree known as the White Coral Tree. This relative of Jatrophas attracts only male butterflies, as its nectar contains a building block for male sex pheramones. (Same c Cestrum diurnum).
Also, grow Strangler Fig (Ficus aureus) in a large pot for the Ruddy Daggerwing. Cool caterpillar that looks like a little dragon. The chrysalis looks like a big green mosquito. The adult butterfly looks like a leaf when it folds its wings. It is orange above and resembles a small swallowtail.
Plumbago will get you a myriad of Cassius Blues.