http://exchange.nagios.org/directory/Plugins/Network-Protocols/HTTP/check_http-perl-script-with-additional-features-%28modified-to-work-with-groundwork%29/details

Written in Perl, many command line options and nice command line help:

check_http_enhanced.pl -H www.example.org -u /somepage -t 1500 \
  -w 999 -w 998 -c 997 -W regexp1 -C regexp2 ...

Default: HTTP 2xx expected, 3xx warn, 4xx critical, 5xx critical,
or use 0 or more -w and -c options to put categorize http codes
as "triggers warning state" / "triggers critical state". Can also
use regexp which trigger states based on content of the webpage.

The patched version uses milliseconds as unit for the timeout.