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Just keep two things in mind:
1) It will only return results for which "dog" is easily discernable. dog.com, dog-helper.org, dog.canines.org, etc., will be returned. Something like bulldog.com will not.
2) It will return results where "dog" appears anywhere in the path, such as widgets.com/canines/dog.htm
You can go to AV and search for url:dog* and you will get urls containing strings starting with "dog." However, you can't search for strings that contain "dog" any-ol'-where -- url:*dog gets you only those URLs which have "dog" as an independent string.
url:dog* gets you over 900,000 results. Since you're looking for domains only, you probably want to use this search: url:www.dog* which will give you 90,000 results or so. To narrow it down even further, include the keyword dogs:
dogs url:www.dog*
which will narrow your results even further.
Another option is to search the Yahoo Directory (http://directory.yahoo.com , NOT www.yahoo.com ) using its url syntax: u:dog . However this will give you a very limited number of results.