Playing chords or special dissonant intervals with arpeggio (fast or slow) to make them sound more expressive
Different tempo of releasing the pedal to get a soft end of a note or chord
Different tempo of releasing the fingers from the keys to get a soft or hard end of a note or chord
Releasing the pedal only partly, so that not all the notes from before get lost.
Movement of the head or upper part of the body to signal a light accentuation (insted of really playing louder)
All sorts of movements with the hand/arm (forwards, upwards, downwards, away from the keybard) in different tempi
The most intense effect I love from pianists is, when they play extreme slow and soft pieces and the piano bank produces squeaking sounds

And something, that is very important for musical expression
for me (some people get very angry about this

) :
Playing series of equal note values
uneven, known as "inegale playing". Uneven playing is extremely important to get the proper expression of many pieces, not only romantic, but also of old music, especially J.S.Bach