Thanks for writing. You didn't mention how tall the boxes are or the growing conditions (sun/shade, soil type, etc.)., so I can't really make any recommendations. But the staff at your local garden center or nursery should be able to. They'll also be able to tell you what's actually going to be available for purchase in your area.
If you want to do a little research ahead of time, check out our Plant Encyclopedia --- it will allow you to search for plants based on a wide range of factors, including hardiness Zone, bloom time, deer resistance, and other factors.
---Justin, Senior Garden Editor, BHG.com