Google now offers so many APIs and services that it is difficult to keep track of them all, or to even take heed when new ones are offered. Google's engineers may have realized that this is a problem, because they have recently created a nice place to see all of these APIs and services in one glance.
In January, the folks over at Google Code posted this "periodic table of APIS" graphic to allow you to see all of Google's API endeavors at once. Pay special attention to the buttons on the top of the page -- when you mouse over each one (eg Mobile, Data APIs, etc), the corresponding APIs in the table below are highlighted. Clicking on one of the individual "elements" will take you to a page that describes that particular API.
Check it out here: