It's Thomas Tallis' version, and here's the mp3.
About the song, including the words, again, from Wikipedia:
O Sacrum Convivium is a Latin prose text honoring the Blessed Sacrament. It was written by Saint Thomas Aquinas. It was included in the Latin Catholic liturgy as an antiphon on the feast of Corpus Christi. Its sentiments express the profound mystery of the Eucharistic miracle: "O sacred banquet at which Christ is consumed, the memory of his Passion is recalled, our souls are filled with grace, and the pledge of future glory is given to us."
Original Latin (punctuation from Liber Usualis):
O sacrum convivium!
in quo Christus sumitur:
recolitur memoria passionis ejus:
mens impletur gratia:
et futurae gloriae nobis pignus datur.
Translation of original Latin:
O sacred banquet!
in which Christ is received,
the memory of his Passion is renewed,
the mind is filled with grace,
and a pledge of future glory to us is given.