Thank you very much for that list, TmT.
http://teachers.net/mentors/spanish/ - I have come across this one before. It's simple to use but it doesn't do what I would like a network to do: promote the teachers. It appears to leave them isolated.
http://www.csun.edu/~hcedu013/eslsp.html - This page appears to have a glitch in it... as I scroll down the letters get bigger and bigger. Enormous, in fact.
http://forums.theteacherscorner.net/forum.php - I like the look and feel of this one. It's not exclusively for Spanish teachers.
http://forums.atozteacherstuff.com/ - A very well populated forum, again for teachers in general. There are so many posts it's easy to find a number which are Spanish related.
http://teacherfocus.com/ - Another busy forum for teachers of all subjects.
This is all very useful for my research into the possibility of starting up a forum just for Spanish teachers, so thanks again - ¡Muy interesante!