Here are links to a number of websites that discuss and refute the tradition of tithing. Some offer free downloadable books and articles on the subject. I do not necessarily agree with (nor am I aware of) every doctrinal position held by the publishers of these sites, nor would I expect them to agree with mine. 

• SHOULD THE CHURCH TEACH TITHING? A Theologians Conclusions about a Taboo Doctrine.  An exhaustive study at the textbook level by Russell Earl Kelly, Ph. D.
• THE TITHING DEBATE
• THE TITHING DILEMMA
• Tithing Today: God's Plan or Designs of Man?
• TITHING: Low-Realm, Obsolete & Defunct
• Truth or Tradition:Tithing vs. Giving
• L. Ray Smith on tithing