Web
IAWiki-Card Sorting (Excellent resource page for Card Sorting)
Boxes and Arrows (Some great Card Sorting articles)
Information Design using Card Sorting
Cluster Analysis

Books
C. Wodtke: Information Architecture - Blueprints for the Web (P.104)
J.J. Garrett: The Elements of User Experience
L. Constantine, L. Lockwood: Software for Use (P.83)

Other Card Sorting Softwares
EZSort (Most popular Card Sorting Software)
CardZort (Nice tool with an own Analysing Software)
WebSort (Web-based Card Sorting)
WebCAT (Web-based Card Sorting; has to be installed manually)