Google attributes certain websites "Sitelinks" and at the SEW forums, I found an interesting discussion on what it is that causes this. It's all speculation though, so I've decided to start a research project on what factors in Google's data/algorithms might cause these Sitelinks to appear.
The first thing I've done has been to establish a methodology of possible factors to test for. Second, I've created a sample set of 100 sites that have Sitelinks. Here is the list of sitelinked sites:
Atu2 Kidsastronomy General Motors McGill University of Toronto Kraft Omniture Insurance.com Sierra Club MSN Yahoo Goog SEW SEL SEObook SEOmoz Squidoo TD Canada Trust Parliament DoubleClick 24/7 Real Media Loblaws Xbox360 Forum Loreal KidsDinos Biology4kids CoolMath4Kids Genealogy.com Ancestry.com PlentyofFish Problogger Vistaprint Logos.it Blue Host Hostgator Mortgage101 Tiger Direct Law.com Microsoft Adobe PlanetPhotoshop W3C ScienceMag Journal of Medicine Journal of Psychiatry Journal of Biological Chemistry American Bar Association Beckett Alibris Digg Stumble Upon Media.com Fox TV Canada.com Conservative Party of Canada Liberal Party of Canada Green Party of Canada Food Network Scholarships Canada Standford newspaper London England – VisitLondon.com comes up below news results and below Maps results with Sitelinks. Toronto Canada – Toronto.ca below maps CollegeHumor Download.com IGN.com Counter-scipt.net – Counter-strike scripts Feedreader.com Newsgator CTV – CTV.ca comes up after a futher query link to Google finance and stock info TSX.com for Stock Berkshire Hathaway Mohawk College – Mohawk How Stuff Works Kids Health Victoria’s Secret Myspace Alexa Facebook LinkedIn Technorati Sitepoint DigitalPoint V7n Compete Bargain.com HaAretz Yediot Ahronot Pajamas Media Vertrue Consumer Reports Shareasale CJ.com Namepros Olive Garden Gardeners – Garden Supply Shoppers drug mart (but not Pharmaprix) Creditcards.com ISEdb Pandia WebProNews
It's a pretty prestigious group, I think we can agree. I'll be conducting tests over the next weeks and months to figure out what the Sitelinks attribution factors are. Stay tuned for more. In the meantime, try typing in the name of your favourite site into your Firefox address bar. You'll find that those sites that have sitelinks will see their site show up right away; some others will return a Google results page (there's a grey area where sites have no sitelinks but they do get returned automatically in Firefox.