LATVIA: These days there aren't much active websites and forums (and so does explorers..) But those who remains active , are very experienced and can tell about places which aren't described on websites. And there are lots of great locations, of course. And yeah, i am from Latvia, so you can ask everything
http://www.post-apo.lv http://wwww.bradajumi.lv (these days useful mostly gallery:
http://www.bradajumi.lv/gallery/http://www.grauzti.lv http://www.diggfiles.lv http://www.diggers.lv ESTONIA Estonia is located near Latvia and it's even smaller than Latvia. It's a pity i don't know much information about Estonian urban exploring forums. There's one = forum, called
http://forum.diggers.pri.ee/and another one
http://www.urbex.ee/but there's one breath-taking Estonian photographer forum, kind - of UE related:
http://www.karelkravik.com/ LITHUANIA At the moment, i guess Lithuanians has the most active explorers between Baltic countries. Also, they have great locations.
Some really great forums which i highly recommend:
http://www.pamirsta.lt http://www.niekonaujo.lt POLANDhttp://www.forgotten.pl Lots of places but the most important thing is that every member can make something like a "status update" for a place, very useful details.
PS
Guerrillaexplorer066 , thank you very much for creating this thread. Now i know more about Finland and Poland.