http://arcfn.com/
http://arcfn.com/doc/index.html
http://www.lisperati.com/
http://www.lisperati.com/arc/regex.html
http://www.fnargs.com/
Look at submissions by your favorite leaders:
http://arclanguage.org/leaders
There are plenty of other great contributions out there but this will get you started and covers the major sites that I can recall offhand. Other good links anyone?
anarki is at http://github.com/nex3/arc and it's world-writable, lots of people share code there
-----