tedster - 9:18 pm on Jan 27, 2011 (gmt 0)
That is the question indeed. If you can access data about domains that share IP address and compare that with domains that are owned by the same party that gives you a start. Almost no one keeps a redirected domain name on a dedicated IP address.
Also, occasionally you can find 301 redirects listed as backlinks on various tools - but you can't depend on that source for accuracy or thoroughness.