Greg Robinson, who I had the pleasure of meeting at Autodesk some 11 years ago in the run-up to Release 14, has started a Wiki for AutoLISP and other AutoCAD-based source code. I’m a big fan of LISP in AutoCAD, so I’m happy to see this resource available for users.
It’s in its infancy right now, but if you pick the All Pages link you’ll see that there already dozens of routines available, one of which may help you with something you need to do. Here’s the link to the main page: