The WLC documentation would make it appear (or maybe previously) you should download a sample web auth bundle code from the WCS Templates. I was never able to find a sample .tar file on the WCS 188.8.131.52 templates.
However I found on Cisco.com under Support > Downloads > Products >Wireless> Wireless LAN Controller Standalone Controllers> Cisco 5500 Series Wireless Controllers > Cisco 5508 Wireless Controller > Wireless Lan Controller Web Authentication Bundle-1.0.2 > webauth_bundle-1.0.2.zip
It was updated in June 2011, some pretty good sample html code.
The readme.html in the sample webauth_bundle-1.0.2.zip file has been very helpful , almost as good as the suppport community web page on custom web auth.