Anyone have a good on-line reference for mastiff looking dogs?

Answer 1

Try this one - it has a list of dogs divided up by weight with clickable links to more information & photos:

http://www.pgaa.com/canine/general/size.html

The article in Wikipedia might also help you:
http://en.wikipedia.org/wiki/Mastiff

This article has loads of different types of mastiff listed:
http://www.suite101.com/article.cfm/english_mastiffs/113374

Best wishes

Answer 2

http://www.moloss.com/001/ptxt/breed.html

Check out this site. It's called mollosser world. The mollosser is supposedly the ancient breed of dog that is the common ancestor for all the mastiff type dogs of today. The link is to their breed page.

Answer 3

Try www.dogo.org.

However, the Dogo is a particularly aggresive breed.