Google Draw- I've seen google draw but haven't spent a lot of time exploring all of what it can do. I can honestly say Google Draw will get more use from me in the near future it has some great capabilities.
Kainzena- is a google doc add-on that allows you to leave audio feedback on a google doc.
Highlight Tool- is a google doc add-on that allows you to create highlighting categories into a google doc (picture below)
Formlimiter- is a google form add-on that allows you to set a time and date to turn a google form off.
Choice eliminator- is a google form add-on that allows you to make choices disappear once they have been selected. This would be great to use when scheduling conferences.
SiteMaestro- is a google spreadsheet add-on that allows you to see more specific information regarding who made what edit and when.
Conceptboard- is a google extension that acts like a whiteboard program but has the ability to make the "whiteboard" much larger and wider than a regular doc or google draw product.
Picasa- Is an extension that enables facial recognition to rage photos from within your drive. This is a really cool extension if you are at all interested in making a collage or a slideshow. I highly suggest looking at some examples on youtube.