It's most obvious in the Christmas Oratorio
http://youtube.com/watch?v=sV6O1JCWDd8
http://www.jsbach.org/bwv248.html
http://oll.libertyfund.org/index.php?option=com_content&task=view&id=1120&Itemid=288
No. 21.
Receive me, my Redeemer (Erkenne mich, mein Huter)
http://oll.libertyfund.org/?option=com_staticxt&staticfile=show.php%3Ftitle=2055&chapter=149340&layout=html&Itemid=27
O Haupt voll Blut und Wunden
http://youtube.com/watch?v=B4JYwbWwNSs&feature
This song is notable for being based on a melody line from Johann Sebastian Bach's chorale from "St. Matthew Passion," itself a reworking of an earlier secular song, "Mein Gmüth ist mir verwirret," composed by Hans Hassler.
http://www.youtube.com/watch?v=l_sl4r0eGVY
http://www.songfacts.com/detail.php?id=7447
http://en.wikipedia.org/wiki/American_Tune
http://music.minnesota.publicradio.org/features/0104_passion/