http://www.uvm.edu/~ngotelli/nullmodelspage.html
The textbook on Null Models that is the basic source of reference in the field. Now out of print, courtesy of Smithsonian Press it has been made unvailable
online on Nicholas Gotelli's webpage, chapter by chapter.
Smantel (Katrin Böhning-Gaese)
http://www.oekologie.biologie.uni-mainz.de/commecol/main.html
This is a specialised program tackling the problem of autocorrelation when analysing similarity of communities. The Signed Mantel test evaluates the relationship between two or more distance matrices to test the possible autocorrelation of the trait variables. The programme comes with a complete user guide.