For those who can still get their congregations to add a service this week:
Here is the 1945 Minhat Todah- Service for Thanksgiving Day, Congregation Shearith Israel, NY by Rabbi David de Sola Pool.
Happy Holiday- Let me know if anyone uses it.
Thanksgiving Service- 1945 Rabbi de Sola Pool (pdf of full service)
There are several good sermons from Rabbi Leo Jung for Thanksgiving Sabbath and a couple of shiurim on the web from Rav Soloveitchik from the Wednesday on the eve of Thanksgiving. Here is one of my favorites from Nov. 22, 1975
Update 2017
in 2016, I posted a 1905 service for the Sabbath before Thanksgiving written by Rev H. Pereira Mendes of the Spanish- Portuguese synagogue of NY
And in 2014, I posted the Thanksgiving service from Kehilath Jeshurun 1940 and prayer from Rabbi Joseph Lookstein.
The Book of Doctrines and Opinions: 