Ann Smarty at Search Engine Journal has recently recommended SpyOnWeb. SpyOnWeb is a utility which allows you to submit a URL, IP address, Google Adsense ID, or Google Analytics Code ID to a query engine, and returns a listing of every site associated with each type of query submitted.

IP address for example will return all known virtual hosts assigned to the IP address, where Google Adsense ID will provide you with a list of all known sites running that specific Adsense ID.

Pros:
  • It's free.
  • No registration or login required.
  • It may allow you to see what site(s) on your shared IP may be compromising your standing with the search engines, assuming they penalize you for this.
  • It may give you some insight into your competitors domain, niche, and link building tactics.
  • It may allow you to research who you may be linking to prior to reaching a linking agreement.

Cons:
  • It may not be entirely accurate. Specific instances where accuracy may be an issue: shared hosting provides the same IP address to multiple clients.
  • Competitors may use this utility to out you if your practices aren't entirely ethical.