You may notice that Google sometimes shows additional links under the first search result. For example if you search for InSightec (a company that developed a solution for performing non-invasive Uterine Fibroid surgery) there are sublinks for: 2006 News, High Intensity Focused Ultrasound, etc. These sublinks are called sitelinks by Google. Sitelinks have been around for a while and there has been speculation to when they appear. Google doesn’t explain much other than the fact that they are shown when they think it will be useful to the user. You can read their official explanation here: http://www.google.com/support/webmasters/bin/answer.py?answer=47334&topic=8523.
How to Get Sitelinks
From casual observation, I believe that they are shown when a very high percentage of people click on the first link. In those cases, Google can justify using more real estate for the first search result, which inevitably crowds out other sites. So to get more interior links from Google all you have to do is make sure that your site gets almost all the clicks — easier said than done. One tip is to choose unique names for products and company names. This will help ensure that most people click on your result when searching.