The following sites have 3D puzzles in various formats (cdr, dxf, dwg, gif, jpg, etc)
I've listed them in searchable preference
Using cardboard, I've put together 80+ of these puzzles by hand. My granddaughters like to play with the animals.

All free files | Design Makerspace
B.C. Bones Online :: Download Instructions
LOBZIK - ?????? - ??????? ?????????? ?????? - Woodcraft Construction Kit [????? - ??????????? ? ????????]
Tiere an Land Archives - dxf-downloads.de
Free cnc (dxf) files : CNC
http://www.cnczone.com/forums/misc.p...hments&t=19346
http://www.cnczone.com/forums/misc.p...chments&t=5276

instructions or 3D view
fly
http://www.designmakerspace.com/down...id=3126&file=0

biplane
http://www.designmakerspace.com/downloads/biplane/

mechanical hand
http://www.designmakerspace.com/down...chanical-hand/

sphinx instructions - very good
http://www.youtube.com/watch?feature...&v=PDPxwEYgqsM

PS:
A larger selection of buildings, dinosaurs and aircraft (WWII) would be nice