I took this little lot over the snowy weekend before Christmas, they are all either stations or within easy walking distance of, may or may not be as good in normal weather conditions though!
http://www.redcow.fotopic.net/c1794172.html
Ipswich and Stratford are probably the most popular, as is brantham (long old walk from Manningtree though) and the bridge over the estuary at Manningtree itself, which is on my list to try out. I quite like Colchester as the long platform gives a variety of angles. Although most of the bigger stations are barriered I've not had any trouble, just the odd strange look from normals!
Chalkwell is the 'classic' LTS line location, although various stations en-route arn't too bad either.
Personally I'd stay away from local stations south/west of Shenfield and Cheshunt, but thats probably just me...
Mr Ferret, give me a bell if u are down in the area!