Select next/previous keyframe

or

Select next/previous track

or

Play a scene beginning at the current
time cursor location

Enter (numerical keypad)

Stop scene playback

0 (numerical keypad)

Create a new keyframe

Ctrl -click a time track

Duplicate a keyframe

Alt -drag keyframe

Create an action placeholder

Ctrl -click action on action track

Scale an animation while maintaining the relative time positions of all keyframes on the same time track

Ctrl + -drag