All zinnias are GREAT for Butterflies. Really any will do. I really love large zinnias, the California Giant Zinnas are a great heirloom-type. I also like the cactus zinnias, as they often can be huge and beautiful with raggedy twisty, very retro or old fashioned looking. As are the Persian Carpet and Whirligig types. Really any mix will do. Plant according to how tall you want them and your personal color tastes.

If you scroll down Renees has some great pre-mixed varieties, Granny's Boquet is very nice.

http://www.reneesgarden.com/seeds/seeds-hm/flowersT.htm#bling

Tithonia, "Torch" or mexican sunflower is a HUGE plant but if you have space elsewhere is also a butterfly magnet.

Together our entire garden was filled with swallowtails all summer. 40+ butterflies every morning.

The seedheads also attract many beautiful goldfinches at the end of the summer....a treat to watch!