ExelisVIS www.ittvis.com is the developer of IDL.  ExelisVIS maintains links to other sites, a user code base, and a tech support page.

David Fanning (www.dfanning.com) is one of the great IDL teachers and writers. His web site has dozens of excellent example IDL programs.

Craig Markwardt (http://cow.physics.wisc.edu/~craigm/idl/idl.html )  has some absolutely outstanding curve fitting and array manipulation routines.

RIck Towler (http://www.acoustics.washington.edu/~towler/)is one of the experts in IDL 3D object graphics. His camera object is a regular part of all our projects.