Jon Primrose maintains a very complete glossary of stagecraft terms,
acronyms and jargon at http://www.ex.ac.uk/drama/tech/glossary.html

The historical costuming FAQ can be found at
http://www.jcave.com/~dybitter/faqs.html

The rec.audio.pro FAQ can be found at
ftp://rtfm.mit.edu/pub/usenet/rec.audio.pro/

There's a list of stagecraft resources at
http://www.yahoo.com/Arts/Performing_Arts/Theater/Stagecraft/

The stagecraft list archives at
http://www.ffa.ucalgary.ca/cgi-bin/wais-stgcrft.pl have a good selection
of info

The Society for Creative Anachronism have a lot of useful information
for historical costuming, props and production at
http://www.pbm.com/~lindahl/arts_and_sciences.html

The page for costuming info is http://users.aol.com/nebula5/costume.html

Theatre Crafts International have a good selection of tips and howtos at
http://www.etec.org/tci/howtos/howtos.shtml