Hello Chris,
If you're using Admin Tools for ArcGIS Online, we have a tool that does what you ask. Under the Users Tools, there is a tool in the far left column called Export Users to CSV. Comma Separated Values (CSV) is a format that can be opened by Excel or any other spreadsheet software available today.
When you use the Export Users to CSV tool, it first prompts you for the users you want to export (Hint: checking the checkbox at the top of the table will check all the users). Next, it prompts you for the fields to export. Fields include user names, first and last names, and the level. Finally, the tool will prompt you to confirm your selection. Upon confirmation, it will download the data and package it into a CSV file.
Export Users to CSV is available in both our free and professional versions.
Hope this helps,
Ken