A clever Mac developer reverse-engineered the API for Spotlight to give us the ability to get Google searches rather than Bing when using Spotlight in Yosemite.
The application is called Flashlight and can be downloaded by visiting the page found if you click the name or the image above.
Big thanks to Nate Parrott and many others who have contributed to the project. You may also download the source code at GitHub.
There are more than 100 plugins for this tool - if you find Spotlight as useful as I do, you’ll definitely love Flashlight!
UPDATE: to develop a plugin, check out the instructions provided here.