Apart from the theme of the modern existential crisis, what are some other dominant themes and motifs in T. S. Eliot's poem "The Lovesong of J. Alfred Prufrock?

i agree with mr. pedro  brites

In addition to the existential , metaphysical anguish of the modern man , Prufrock also typifies helplessness , uncertainty in a totally incomprehensible world. The arbitrariness and irrationality of a dream world inhabit prufrock's consciousness  leading him to chaos , disorder , monotony , emptiness and ennui where streets seem to be following with ' insidious intent ' and the evening fog takes on the hallucinatory image of a cat. The hollowness of the modern civilization is suggested when ' in the room women come and go / talking of Michael Angelo. These women are intellectual snobs having no idea about the power of his paintings.  Prufrock tries to ward off the horror of the inevitable ( I grow old I grow old ) by measuring out his life with a coffee spoon and in doing so he makes a caricature of himself. Both Guido da Montefeltro and Prufrock are in the same situation . The former is in the8th circle of hell and the latter is in a death -like situation where everything leads to inaction. Let us go then you and I ......and then nothing happens. The question is who is this 'you'.  

The futility, the emptiness of faith, sensorial experience of the death..