Last night I was talking to a group on Half Fanatics about my 50 by 50 Challenge. One of the runners sent me a like to a 50 Staters Gadget. This is the coolest thing. It will help you calculate how to do back to back races in the same weekend to help you get the 50 half marathons in 50 states sooner.
You have all kinds of options to narrow down your search. You can select how far apart your are willing to drive between cities, and it will tell you on the right column how far you have to drive between cities.
I thought I would share.