PocketRadiologist Head and Neck Top 100 Diagnoses by Harnsberger (Amirsys) Hardcopy and PDA versions are handy quick reference.
Handbook of Head and Neck Imaging also by Harnsberger (Mosby) paperback, inexpensive and very useful. Just diagrams, no actual radiographs.
Recommendation for book buying:
Walmart.com - consistently cheaper than anybody else
mysimon.com - compares several online bookseller prices
loginbookstore - get on their periodic email listing of new titles
ecampus.com - good discount, mostly free shipping