Sri Chinmoy

This is very beautiful (and very sad, sadness is often akin to beauty...) poem, called "The Eye of My Eye":

By whose touch does the lily smile

And open its beauty – bud?

Whose moonlit beauty

Do I see in the lily?

Who is the Eye of my eye;

Who is the Heart of my heart?

Alas, then why do I not see Her,

Her face of transcendental Beauty,

Even in my dreams?

Rabindranath Tagore

I like a lot this, very concise and mystical, definition by Tagore:

"Beauty is truth's smile

when she beholds her own face in

a perfect mirror."

Lord Byron (from 'Don Juan')

Her glossy hair was cluster'd o'er a brow

Bright with intelligence, and fair and smooth;

Her eyebrow's shape was like the aerial bow,

Her cheek all purple with the beam of youth,

Mounting, at times, to a transparent glow,

As if her veins ran lightning.

Visvanatha
The experience of beauty is pure, self-manifested, compounded equally of joy and consciousness, free from admixture of any other perception, the very twin brother of mystical experience, and the very life of it is supersensuous wonder... It is enjoyed by those who are competent thereto, in identity, just as the form of God is itself the joy with which it is recognized.

Ryo-Nen

[What follows is the very last composition of a Zen nun, who had been in her youth a great beauty and a great poetess:]

Sixty-six times have these eyes beheld the changing scenes of Autumn.

I have said enough about moonlight.

Ask me no more.

Only listen to the voice of pines and cedars, when no wind stirs.

Lord Byron (George Gordon Noel Byron)

The nameless charms unmark'd by her alone.

The light of love, the purity of grace,

The mind, the music breathing from her face,

The heart whose softness harmonized the whole,

And, oh! that eye was in itself a soul.

Johann Wolfgang von Goethe
Beauty is at once the ultimate principle and the highest aim of art.

Bernard de Bovier de Fontenelle
A beautiful woman is the hell of the soul, the purgatory of the purse, and the paradise of the eyes.

Rabi Al Basri's prayer
God, if I worship You in fear of hell, burn me in hell. And if I worship You in hope of Paradise, exclude me from Paradise; but if I worship You for Your own sake, withhold not Your everlasting Beauty.