Here's a list of stores where you can (at least for the time being) buy signed copies of both Looking for Alaska and An Abundance of Katherines.

Books & Crannies
15 South Madison Street
Middleburg VA 20118
540-687-6677
http://www.booksandcrannies.com/

Lake Forest Bookstore
680 North Western Avenue
Lake Forest IL 60045
847-234-4420
http://www.lakeforestbookstore.com/

Cover to Cover
3560 North High Street
Columbus OH 43214
614-263-1624
http://www.covertocoverchildrensbooks.com/

Blue Willow Bookshop
14532 Memorial Drive
Houston TX 77079
281-497-8675
http://www.bluewillowbookshop.com/

University Books
990 102^nd Avenue NE
Bellevue WA 98004
1-800-335-7323
http://www.bookstore.washington.edu/

Secret Garden
2214 Northwest Market Street
Seattle WA 98107
206-789-5006
http://www.secretgardenbooks.com/

I believe that Chicagoans can also get signed books at the Book Cellar in Lincoln Square. These are all great independent bookstores, and I'd like to thank them for helping make my tour such a blast.