Maybe we should stop trying to guess the next Google services. What's next for Google is right here on a big whiteboard from their GooglePlex. The photo was taken last year by Niall Kennedy and includes a small part from their master plan. As you can see many projects that don't have a tick in the whiteboard have been launched.
A bigger and more comprehensive image is available here, but it's not very clear.
As you can see, there are a lot of verticals and new domains: travel, health, TV, games, reviews, marketplace, dating, real estate, jobs, mortgage, pets, music and many ambitious projects like redesigning TCP/IP, and HTTP and creating a new generation of web based on BitTorrent.
Other pieces from the puzzle (half jokes, half serious projects):