in reply to The great ball of mud
Big Ball of Mud has its roots in Ralph Johnson's group at the University of Illinois, Urbana. (Johnson is one of authors of Design Patterns.) A lot of very influential thinking sprang from the circle that formed around Johnson. (One of his grad students implemented the first Refactoring Browser for Smalltalk.) Refactoring in turn formed one of the core practices of Extreme Programming.
The references in Big Ball of Mud are worth mining for other good reading. There's also a Big Ball of Mud page on Wiki that has some extra words by Brian Foote, plus a few good pointers.