After having answered the same question repeatedly about Sitelinks I've decided that perhaps this is a good topic for the blog, at least this way I'll be able to direct people to a single location to find all the answers regarding this confusing area. Sitelinks is the name given to the links that appear below the #1 result for some Google queries.
An example of Sitelinks can be seen when we run a search on Google for "AOL":
Here we can see links to internal pages on the AOL website. So how do you get Google to do this for you? The answer, at present is, you don't.
Here is what Matt Cutts wrote about it:
For a small number of sites, we are not just showing our regular snippets: we try to expose useful links from within a site. In this Berkeley example, Google shows links for Berkeley departments, academics at Berkeley, etc. Pretty neat (and more importantly, useful) stuff.
People who know Google well will go “Cool” and move on. Other folks will ask things like “Are sites or their links selected by hand–can my site get in on this? Is money involved?” And the answer is: it’s all algorithmic. The algorithms pick the sites where this could be helpful. Of course money isn’t involved at all.
So it's an algorithm, much like the ranking algorithm but with more mystery regarding how to get it for your site. Here is the only "for sure", you need to hold a #1 position for a phrase. OK, that's easy enough right. Past that there is more myth than fact about what the "secret recipe" is. Guesstimates range anywhere from site age to the internal linking structure in how the list is generated and whether it is at all for a query.
Here is what
Google has to say on this topic:
How do you compile the list of links shown below some search results?
The links shown below some sites in our search results, called Sitelinks, are meant to help users navigate your site. Our systems analyze the link structure of your site to find shortcuts that will save users time and allow them to quickly find the information they're looking for.
We only show Sitelinks for results when we think they'll be useful to the user. If the structure of your site doesn't allow our algorithms to find good Sitelinks, or we don't think that the Sitelinks for your site are relevant for the user's query, we won't show them.
At the moment, Sitelinks are completely automated. We're always working to improve our Sitelinks algorithms, and we may incorporate webmaster input in the future.