Digital-Dive - where you can rent underwater camera housings & flashes
Christoph Kaula & Jessica Winter - two very talented nature photographers & biologists
DeepGreenPhoto.com - very interesting site about two german zoologists / photographers
Greg Basco - specialised in rainforest photography, he has amazing stuff on his site. I follow his blog and can recommend his e-book "The Guide to tropical nature photography".
Mediterranean / Italy / Elba: Unica Diving - relaxed diving in the mediterranean sea
Germany: Nachdenkseiten - eine der wenigen kritischen Nachrichtenseiten