Here are some beautiful quotes from the Maitri Upanishad:
Even as fire without fuel finds peace in its resting-place,when thoughts become silence the soul finds peace in its own source.
Samsara, the transmigration of life,takes place in one's own mind.Let one therefore keep the mind pure,for what a man thinks he becomes:this is a mystery of Eternity.
A quietness of mind overcomes good and evil works,and in quietness the soul is One:then one feels the joy of Eternity.
If men thought as God as much as they think of the world,who would not attain liberation?
The mind should be kept in the heartas long as it has not reached the Highest End.This is wisdom, and this is liberation.Everything else is only words.
Words cannot describe the joy of the soulwhose impurities are cleansed in deep contemplation- who is one with his Atman, his own Spirit.Only those who feel this joy know what it is.(all quotes taken from the Maitri Upanishad, 6.24)
The last two are my definite favourites. This translation is by Juan Mascaro; the Nobel prizewinning Bengali poet Rabindranath Tagore said of his translations that they had 'caught from those great words the inner voice that goes beyond the boundaries of words'. As well as the Upanishads, he translated the Bhagavad Gita, spending 20 years in the process and revisiting some verses as much as 20 times before he was satisfied. He also translated the Dhammapada, an important text in the Buddhist canon.