Crepe Myrtle (Lagerstroemia 'Muskogee') is one of the most widely grown crepemyrtles in existence. When you see a 25' tall light lavender crepe myrtle growing on the side of the highway it is almost certainly a Muskogee.
Another possibility for you would be
Crepe Myrtle (Lagerstroemia 'Biloxi') which tends to be a bit more on the pink side of the color range.
One more way to tell them apart: the bark on Muskogee will be a bit grey while the bark on Biloxi will be more of a tan/brown color.
