It could be the native redbud tree.

Here is a link that might be useful: Redbud

Could be purple leaf plums, as well.

Here is a link that might be useful: check it out

Are you sure that it's not a wisteria vine that happens to be growing in a tree?

Eureka! They're redbuds! You would think I would have recognized them, since I have been pulling baby redbuds out of the lawn for two years, but I only know them by the leaves. I'm getting better at spotting different trees since we moved here. The first time I invited one of my friends over to see the house, I told her to turn left and drive past the beautiful rows of crape myrtles to get to our place, and when she got here, she told me that those beautiful crape myrtles were bradford pears!

The ones in our yard look a bit more purple than the photographs, though. Methinks it's time to do a little spring window washing!

Thanks for the brainstorming, y'all!

Cersis canadensis (Redbud) also comes in Purple Pansy that is more purple in flower and leaf color.

Actually that cultivar is called "Forest Pansy".

I might be able to save you some window washing. Your trees are most likely naturally a bit different in color. The color of this tree is pretty variable. You will see all kinds of shades of purple as you drive around.

Oops~~I did mean to type Forest Pansy~~what was I thinking??? Thanks Esh.

Tamibeep - stop pulling out baby redbuds and pot some up. I'd love one!

Rose

Really? Shoot, I'd be happy to pot one up for you, Rose. We have them coming out of our ears. It never occurred to me to do anything other than get them out of the way ever since I let one go for a year and the root system broke up the patio. (whoops.)

We also have a whole bunch of poison ivy, if you're interested... ;o)