It's amazing how one can fill a whole page rhapsodizing about trills. But for me they are more OPERATIC, as if a splendid soprano were singing a Mozart aria, producing the most artfully beautiful alternation of two notes. These would be undulating, and grouped in such a way, that their lilt would be apparent. In fact, they could not be typewritten, because a singer would not use her fingers. Yet if we transfer the figure to the piano, many players will approach trills as static notes, without dipping or shaping them as a vocalist would.
In two videos, I attempt to rise above the mechanics of tapping neighbor notes back and forth, and "sing" through my trills by grouping them in my mind, knowing what I want to hear. In baby steps, I play through slow measured trills, artfully moving into tempo with grace and beauty. (listening attentively)
From the last 2 measures of Mozart Sonata in C, K. 545 (Exposition)
http://youtu.be/MW7uq94rI00
http://youtu.be/oitBy7Wcz7k