Elements of algebra and algebraic computing
by John D Lipson
http://www.amazon.com/exec/obidos/tg/detail/-/0201041154/102-9323252-8541741?v=glance

Categories for the Working Mathematician (Graduate Texts in Mathematics)
by Saunders Mac Lane "Category theory starts with the observation that many properties of mathematical systems can be unified and simplified by a presentation with diagrams of arrows..."
http://www.amazon.com/exec/obidos/tg/detail/-/0387984038/102-9323252-8541741?v=glance

Categories for Types (Cambridge Mathematical Textbooks)
by Roy L. Crole
http://www.amazon.com/exec/obidos/tg/detail/-/0521457017/102-9323252-8541741?v=glance