(in no particular order)
Auran's CONTENT CREATOR's GUIDE (2006)
An introduction to signaling from Chuck Brite. Excellent beginners tutorial about signals and signaling.
Ianz Trainz from Ian Manion (vulcan). He has a large amount of ships, ferries, oilrigs, bridges etc. Many animated/drivable objects. They are of course on DLS, but a lot easier to check them out here, because of the pictures. There is extensive documentation, including how-to-use for most objects. Also a number of great tutorials.
Neoklai's Website from Neoklai Neoklaev (neoklai75). This Page is in russian! This can be somewhat tricky to maneuver around in, so I made this little manual for his site. He has some absolutely awesome animated people and other things. Unfortunately he also has problems at the moment loading them to DLS, so this is the only place to get them for now.