In addition to several books that have been written about sed
(either specifically or as chapters in books which discuss
shell programming), one can find out more about sed
(including suggestions of a few books) from the FAQ
sed-users mailing list, available from:
Also of interest are http://www.student.northpark.edu/pemente/sed/index.htm and http://sed.sf.net/grabbag, which include sed tutorials and other sed-related goodies.
sed-users mailing list itself maintained by Sven Guckes.
To subscribe, visit http://groups.yahoo.com and search
sed-users mailing list.