It is true that the Methodist Center contains what purports to be the dessicated thumb of famous Methodist evangelist George Whitefield. Nobody knows how it got there, though various 'relics' of Whitefield were apparently pilfered from his tomb. The thumb lives in a glass display case.
The thumb has also been featured in Christian History and Biography (Winter 2004) and The Chronicle of Higher Education (October 28, 2005).
That's the only actual body part, although the Methodist Library does have Wesley's death mask (making death masks was actually a fairly common 18th-century way of memorializing the dead). Also, the archives of the Greater New Jersey Annual Conference, which are in the Methodist Library building, have the shoes of a woman who was struck by lightning and survived.
– Adapted from a blog post by Jennifer Woodruff Tait, former Methodist Librarian
Resources
"Bring me the thumb of George Whitfield," Christian History & Biography, Issue 81 (Winter 2004), page 9.
Scott Carlson. "What's the Most Unusual Item in Your Special Collections?" Chronicle of Higher Education, Vol. 52 Issue 10 (10/28/2005), page A6.
Thomas A. Tweed, "John Wesley Slept Here: American Shrines and American Methodists," Numen, Vol. 47, No. 1 (2000), pp. 41-68.