This is not meant to be an exhaustive list of data sources, but is some of the more common ones.
Have you discovered a good data source and want to share it? Email email@example.com and have your source added to this guide,
These are resources or sources for data that may not be thought of as frequently as other resources.
Also, remember that many associations and organizations for industry professionals will keep statistics and data on topics pertinent to the industry. Oftentimes, these are reserved for members only, but some make their numbers freely available to anyone. Another thing to keep in mind is that these numbers may not be collected each year and, if they are, it may take a year (or two) for the numbers to be made available.