Here’s President Bush’s 2006 Thanksgiving Proclamation, which contains two explicit references to God and one mention of "our Lord." There are four variations on the words blessed and blessing and two references to prayer.
GWB’s, by the way, are far from the most explicitly religious--that honor might actually go to FDR’s, though they’d have a few competitors. On the other hand, nothing surpasses the sheer banality of Richard Nixon’s 1971 proclamation:
One of the splendid events which shape man’s destiny occurred when a small band of people, believing in the essential sanctity of their own being, went in search of a land in which their individuality might be the highest national value, before any arbitrary limitation or duty placed upon some men by the whim or design of others.
They went in search of a land where they might live out their own commitment to their own ideal of human freedom. In the purpose of their search, the human spirit found its ultimate definition, and in the product of their search, its ultimate expression. They found the land they sought, and it was a difficult land, but it was rich. With their sacrifices they brought forth its riches, and laid the foundation for a new nation.
We now know the inspiration for Justice Anthony Kennedy’s ruminations on the mystery of human life.
Update: The new and improved version of my meditation on the significance of giving thanks can be found here.