A tiny example wordlist is included with the cracklib package
itself. A very large dictionary suitable for use with cracklib
is also available from the github repository

https://github.com/cracklib/cracklib

Other sources for word lists include:

	http://wordlist.sourceforge.net/

	http://www.openwall.com/wordlists/

Please note, the licenses on some of those word lists are
restrictive, so please read the licenses before redistributing them.
The cracklib-words distribution from the cracklib sourceforge
project page has been built solely from word lists previously
distributed with cracklib or crack packages and/or public
domain word lists.

For best results, supply cracklib with as large a wordlist as you 
have available to you - blackhats brute forcing passwords have those
same lists, might as well use it to benefit your security.

There are HUGE (multi GB) wordlists available online with questionable
sources, but if you are looking for the most complete source, those
would be worth investigating. One collection of them here:

	https://github.com/danielmiessler/SecLists/tree/master/Passwords/Common-Credentials