I have needed many LISP routines over the years and the most bang for the buck comes from the ones that perform little functions that are (for some reason) not part of AutoCAD. In the process I have created many and gotten many from others who have posted them on the web or way back when, on Compuserve (am I dating myself?).
The ones that have served so well have been those small little routines that have fixed something or reduced the number of clicks that I have to do to get something done.
Here are some places to look for AutoLISP code…
http://new.cadalyst.com/code/  – the Cadalyst extensive library
http://www.jefferypsanders.com/autolisp.html  – Free stuff
http://home.pacifier.com/~nemi/  – Better than Nothing AutoLisp – has some annoying popups.
http://www.autolisp.com/forum/  – Nice forum of stuff
http://www.afralisp.net/  – Afralisp
And of course the forums on AUGI.com!
You also could start reading up and create your own. It is easy and it is fun.