I tried the cornmeal trick last night. I'll go out and sprinkle some on the hills I see. We've only lived in this house for a few months and I'm quickly learning that the seals aren't very great. I think there's easily a 1/4" gap under the back door.
Thanks for the tips about the cinnamon, I'm going to put some of that on the windowsill behind the sink and around the sink!