Rational UML resource centre

http://www.rational.com/uml/index.jsp

Object Management Group UML Resource Page

http://www.omg.org/uml/

UML Distilled:

Applying the Standard Object Modeling Language

by Martin Fowler,Kendall Scott

Applying UML and Patterns:

An Introduction to Object-Oriented Analysis and Design and the Unified Process

by Craig Larman

 Top Ten Use Case Mistakes

http://www.sdmagazine.com/documents/s=734/sdm0102c/

Use Case Do's and Don'ts

http://www.togethercommunity.com/coad-letter/Coad-Letter-0083.html