Full Disclosure: I am founder of one of the products that addresses this exact problem.
You have vast array of options. As Anand mentioned, on the high end, you can look at HighSpot, Showpad, Seismic, and Docurated. There are also other options for the mid and lower tier market.
Our product Enablix is targeted for SMB market for sales and content enablement. We also have other competitors in play here. I would recommend checking out G2 Crowd and search for Sales Enablement category. You will see the available options.
If you plan to use any of the cloud storage platforms, please tread with caution. You have to make sure you do not cede control of that folder/repository to everyone and keep it under strong quality control. The biggest risk using Dropbox or Google Drive is that they can very soon get busy and unusable. Ofcourse it will be hard to get any usage metrics.