Mozart, K.73b, "Per Pieta, bell'idol mio" - lingering on the word abbastanza, comes in with the horn the second time around
 K.73d, Recitative and Aria for Soprano, "O temerario Arbace" - wow, surprisingly beautiful, especially the third section beginning with "per quel paterno."
K.24, 8 Variations in G on "Laat ons Juichen" - the variations keep getting better as the piece progresses, good fun this piece; I think I must have a bias towards keyboard pieces and arias.  Liking the stuff he produces in these genres better than the symphonic stuff.