Well, I have now watched the "30 Rock" version three or four times, and it's making me laugh even harder every time I see it. But, just so we don't forget Miss Gladys Knight, here's a performance of "Midnight Train" with the Pips from YouTube:
Here's the audio of the Knight original:
And, if only because it is weird on so many levels, Jessica Simpson in duet with Gladys Knight:
Miss Simpson should just forget it ...