O Lord and Ruler the house of Israel, who appeared to Moses in the flame of the burning bush and gave him the law on Sinai: come, and redeem us with outstretched arms.
The Pontifical North American College's version can be found here.
They also sing one of my favourite renditions of the hymn O Come, O Come Emmanuel which is a paraphrase of the 'O Antiphons'
Today's verse is:
O come, O come, thou Lord of might,
Who to Thy tribes on Sinai's height
In ancient times didst give the law
In cloud and majesty, and awe.