Do you have a general route planned out? There are a couple of Mennonite stores in the Finger Lakes that I enjoy very much. Great prices, but they are not decorated in any way - my favorite is a metal pole barn type of building. Lighting isn't great - you'll need to carry fabric to the window or door if you are looking for specific shade! Unfortunately, my favorite shop, in Watkins Glen, has closed.
Sew Pieceful in Campbell Savona isn't huge but has an excellent selection; it's really good for shabby chic or floral.
Love Round Bobbin in Ambler, PA - not far from Philadelphia/King of Prussia/Valley Forge.
Near Tampa FL, I recommend Happy Apple or Rainbow's End.
Some day, I'm going to get to the central/midwest part of the USA!