There are loads of great sites in Essex (lol I could be being a little biased there
). If your interested in sites in Essex eeyore theres a great book out called wild essex
http://www.lopinga.com/htdocs/ISBN%200-9530362-2-7.html. I bet Richard has it
I live on the Essex/ east London border and one of my fav sites is Epping forest, full of amazing history and plenty of old trees
The Lee Valley is another of my personal favs.