Way back in June 2014 I posted a table to logging events by level and category - Salesforce Log Categories and Events by Level.
I was never really happy with the table layout trying to squeeze that much data in. Also, new logging levels keep getting added and several have been shuffled around recently with respect to the level they occur at.
Here is a hopefully simpler revised attempt using lists. It is compiled directly from the Debug Log Levels detail page, so it should be eaiser to keep up to date.
Similar data can be found in the Debug Log Levels documentation. I found at the time of publishing that I had several in my list that didn't appear on that page, such as CALLOUT_REQUEST_PREPARE, USER_DEBUG_WARN, and DUPLICATE_DETECTION_MATCH_INVOCATION_DETAILS.
The levels are cumulative. So everything that appears at the ERROR level will appear at all the lower levels as well. Everything at the WARN level will appear at INFO, DEBUG, FINE, ... and so on.
- Updated for Summer '18 - v43.0