Reuters-21578 collection
http://www.research.att.com/~lewis/reuters21578/

TiMBL
http://ilk.kub.nl/software.html

Weka
http://www.cs.waikato.ac.nz/ml/

J. Ross Quinlan's page (C4.5)
http://www.cse.unsw.edu.au/~quinlan/