The feature is powered by Google Squared and it's not very new. Most of the results were available if you selected "related searches" from the search options sidebar.
"Sometimes when you're searching, you're not just looking for one specific result, you may be looking for a list to start a series of searches. For example, if you search for [greek philosophers], many search results mention well known philosophers like Plato or Aristotle. Typically, searches like these are the beginning of a research task, where you follow up by searching to learn more about each item in the list, in this case each philosopher," explains Google.
Just like the related searches box, the "top references" box lets you try different queries without having to go back to the previous page. If you click one of the related searches, the box is moved at the top of the page and you can quickly preview the results for all the other items.
Google also started to show relevant lists for actors, movies, TV shows, music artists, writers, painters. For example, when you search for [Picasso], Google shows a list of famous Picasso paintings and small thumbnails. Searching for a movie or a TV shows brings a list of actors, searching for a singer shows a list of albums, while typing the name of a writer returns a list of popular books.
Google Squared, Google Q&A, "best guess" results and related searches are just the tip of the iceberg. Google uses its huge index of pages from the Web to extract information, find facts and correlations, create lists and hierarchies, understand the meaning of a query and generate complex answers. At the recent Inside Search event, Alan Eustace said that his title changed from "Senior VP of Search" to "Senior VP of Knowledge" because search is too limiting and Google's goals are much broader. They "go beyond the organization of information to understanding and facilitating the creation of knowledge".