Dude. I don't know if you've heard yet, but the Monarchs need our help.* They have been taking some devastating hits to their population over the last few years. And by devastating, I mean like over 60% of the population just gone. We're talking worse than the Black Death here, people.
Providing adult food sources is a good start - they tend to LOVE Gregg's Mistflower. Other good plants seem to be Shrubby Boneset (also called White Mistflower), a whole host of daisy-like plants (disc shaped that are wide and flat), and even Lantana and Turk's Cap (though it tends to be frequented more by the Fritillaries).
BUT! If you REALLY want to help the monarchs, you'll also plant host plants. Or, in other terms, the plant that the caterpillars will eat (it never ceases to amaze me how many people will plant host plants only to get upset when they're munched down to nubbins by the insect they are hosting). The Monarchs only lay eggs on milkweed plants. And yes, your milkweed plants will be chewed down to twigs. BUT! you'll be helping the monarchs, which is really more important anyway. Gardening for nature is why you garden, isn't it?
Grouping your plants together to create large masses of the same color will help attract butterflies since they are near sighted (that's probably why they like the mistflowers - the plants create a large grouping all by themselves). Plant some milkweeds close by, add some dishes of water with some rocks in them (for the butterfly to perch on)and Voila! Instant Butterfly garden. If you want to get really ambitious, you can add throw out some fruit trimmings, leave one spot of dirt that isn't covered by mulch (for puddling), and a large clumping grass (for protection at night), and you'll have a garden that the Monarchs will flock to.
* okay, right now probably isn't really the time to plant things like milkweed, but it IS time to plant most perennial plants like the shrubby boneset and lantana. Plus some future planning is always a good thing.