Sokal and Rohlf: Chapter 13.11-13.12.
John Verzani's SimpleR notes: Sections 10,11.
Dalgaard: Chapters 5.2,5.5,5.7,5.8.
Wikipedia [ Signed rank test | Rank sum test | Resampling ]
RR Sokal, FJ Rohlf (2011). Biometry, 4th edition, WH Freeman.This text is required.
Everything else is not madatory, only listed as suggestion in case you want to do some additional reading and/or exercises.