I was sent a link to a website "exposing" Calvinism because it contained a bunch of Luther quotes. Many of the quotes I've gone over already, like this one, but I was intrigued by the documentation of this quote found in a pdf e-book (pictured left) from this site:
“Not for a thousand years has God bestowed such great gifts on any bishop, such as those He bestowed on me!” 
 Museum of foreign literature, science and art, By Robert Walsh, Eliakim Littell, John Jay Smith,Published by E. Littell., 1839,Item notes: v.35 1839,Original from the University of Michigan,Digitized Oct 31, 2005, Page 329 http://cc.msnscache.com/cache.aspx?q=72289142394310&mkt=en-US&lang=en- US&w=b2466ad1&FORM=CVREDocumentation
The book cited in footnote 6 is available from Google Books. On page 329 it provides a number of quotes from Luther (without documentation), and uses the quote in this paragraph:
'At Leipsic, at Augsburg, and at Worms, my spirit was as free as a flower of the field.' 'He whom God moves to speak, expresses himself openly and freely, careless whether he is alone or has others on his side. So spake Jeremiah, and I may boast of having done the same. God has not for the last thousand years bestowed on any bishop such great gifts as on me, and it is right that I should extol his gifts. Truly, I am indignant with myself that I do not heartily rejoice and give thanks. Now and then I raise a faint hymn of thanksgiving, and feebly praise Him. Well! live or die, Do mini sumus. You may take the word either in the genitive or the nominative case. Therefore, Sir Doctor, be firm.'This paragraph is from multiple contexts. The sentence, "At Leipsic, at Augsburg, and at Worms, my spirit was as free as a flower of the field" is from 1524. It's found in LW 40:53 (Letter to the Princes of Saxony Concerning the Rebellious Spirit). The sentence about Jeremiah is from a different context also, Against the Heavenly Prophets in the Matter of Images and Sacraments (1525) [LW 40:144]. Then tacked on is a Table Talk comment from 1542.
The historical context of this Tabletalk comment surrounds the death of Luther's daughter. One of the "great gifts" was.... his daughter:
When his daughter was very ill, he said: ' I love her well; yet, O my God! if it be thy will to take her hence, I will resign her, without regret, into thy hands.' As she lay in bed, he said to her: ' My dear little daughter, my darling Magdalen, thou wouldst, doubtless, willingly remain here with thy poor father, but thou wouldst also go hence willingly to thy other father, if he call thee to him?' She replied: ' Yes, my dear father, as God shall please.' ' Dear girl,' returned Luther, ' 'tis not with thee that the spirit alone is willing. He then walked up and down the room for some time, saying to himself, but half aloud: ' Ah, I have loved her dearly! ... If her flesh be so strong, what must her spirit be?'
"He further said, among other things, 'God has not, for a thousand years, bestowed so many great gifts upon any bishop as he has upon me. One should duly appreciate and pride oneself upon such gifts; but—I am mad with myself for it—I do not enough rejoice at them in my heart: I do not sufficiently return thanks for them. I sing, indeed, from time to time, a little song of praise to the Lord, but 'tis very inadequate.' . . . ' Well, whether we live or die, we are the Lord's; so, courage, doctor!' [source]
The actual comment is a Table Talk comment, located in LW 54:430
No. 5494: Illness of Luther’s Daughter Becomes Graver September, 1542
When the illness of his daughter became graver he [Martin Luther] said, “I love her very much. But if it is thy will to take her, dear God, I shall be glad to know that she is with thee.”Afterward he said to his daughter, who was lying in bed, “Dear Magdalene, my little daughter, you would be glad to stay here with me, your father. Are you also glad to go to your Father in heaven?” The sick girl replied, “Yes, dear Father, as God wills.” The father said, “You dear little girl!” [Then he turned away from her and said,] “The spirit is willing, but the flesh is weak [Matt. 26:41]. I love her very much. If this flesh is so strong, what must the spirit be?” Among other things he then said, “In the last thousand years God has given to no bishop such great gifts as he has given to me (for one should boast of God’s gifts), i'm angry with myself that I’m unable to rejoice from my heart and be thankful to God, though I do at times sing a little song and thank God. Whether we live or die, we are the Lord’s [Rom. 14:8]—in the genitive singular and not in the nominative plural.”
The Life and Letters of Martin Luther provides somewhat of a different version:
As his daughter lay very ill, Dr. Luther said: "I love her very much, but dear God, if it be thy will to take her, I submit to thee." Then he said to her as she lay in bed: " Magdalene, my dear little daughter, would you like to stay here with your father, or would you willingly go to your Father yonder ? " She answered: " Darling father, as God wills." Then said he: " Dearest child, the spirit is willing but the flesh is weak." Then he turned away and said: " I love her very much; if my flesh is so strong, what can my spirit do? God has given no bishop so great a gift in a thousand years as he has given me in her. I am angry with myself that I cannot rejoice in heart and be thankful as I ought."