I have another challenge! STALKER: Shadow of Chernobyl OGF models. Here are some resources that should serve as a starting point:
[EDIT 3/8/2008: Removed abakan.zip as the format is now known.]
http://three.homeip.net/files/OGFViewer104.rar - OGF Viewer 1.0.4 (333 KB, for viewing OGF models — no export capability yet)
http://three.homeip.net/files/STALKER_Data_Unpacker.zip - Database Unpacker (56 KB, if you have the game you can unpack the DBA archives)
Personally, I'm not concerned with skeletal animation data. I'm only interested in exporting the mesh and UV coordinates. I'll look at the format when I get a chance and post anything interesting I find, but I'm not too good at this stuff.