The Stopwatch icon next to the Object Properties entry in the Project window turns Automatic Keyframing on and off for each attribute.
You can also use the Stopwatch to clear all keyframes for a particular attribute - just click on it. You will see a warning dialog, click OK, and the keyframes will be deleted.
For more information, see The Stopwatch in Chapter 16 of the User Guide.
You can also shift-click or drag-select event markers along a timeline, then delete them all at once.
NOTE: Do not press the Delete key to delete an Event Marker, this will delete your selected object. Use the backspace key (labeled as delete on many Macs).