Reverse Domain Lookup
Find all domains hosted on one IP address with this fast service.
Official links for Reverse Domain Lookup
- YouGetSignal
Reverse Domain Lookup
Reverse Domain Lookup Review
YouGetSignal gives you a list of all domains and subdomains hosted on one IP.
On Shared Hosting plans this list may be rather long, on dedicated servers there may be only one entry.
See an example query for "seomoz.org" here:

With the tool you can e.g. find out which other sites are hosted on your shared hosting plan. Also you can check if your link partner's links are hosted on one machine. If so, the link values might decrease since Google sees them as redundant.