Here are a few fun tools built in to the Google search engine that I use regularly:
define: If you want to know the meaning of a word like nadir, type "define: nadir" into a Google search box. You'll get results with the word's definition in them.
convert Want to convert mililitres to ounces? Type "convert 240ml to ounces" into a Google search box, and you'll get the conversion in your search results.
Scholar Need to search scholarly texts? Try Google Scholar.
Try this one: Useful Google tools You Have Never Heard Of