There's a lot of them out there and a lot of people here recommend them. But I've never found them to be that great. I guess in a way if you don't know a thing about dogs it's a starting point, but I think a better starting point is one of those big, colorful, all-breed encyclopedias. And from there you can research the breed(s) you're interested in.

So, if you like them, which ones do you think are best?

Here's the ones I've found:
http://us.iams.com/iams/en_US/jsp/IAMS_Page.jsp?pageID=DBS
http://www.urbanhound.com/houndFinder/breedFinder.asp
http://animal.discovery.com/breedselector/dogselectorindex.do
http://www.purina.co.uk/Home/All+About+Dogs/Your+New+Pet+Dog/Choosing+a+Dog/Dog+Breed+Selector.htm
http://www.dogbreedinfo.com/search.htm
http://www.selectsmart.com/DOG/
http://www.puppyfinder.com/breedselector.php
http://www.5stardog.com/dog-breed-selector.aspx
http://www.breederretriever.com/breedselector.php
If I have time later, I'll test them and see if the results comply with my knowledge of purebred dogs. Maybe other knowledgeable dog people can do so as well?