From the NY State Museum:
The Recovery section begins at Ground Zero with a dramatically damaged 20-foot high; 10-ton steel column from floors 71-73 of the WTC North Tower. The stories of the recovery operation at Fresh Kills are told through the many objects found in the mountains of debris, including material from the everyday life of the buildings, the steering wheel from a car, Observation Deck souvenirs, melted floppy discs, keys, and a crushed payphone. A large collection of firearms from WTC Building 6 are on exhibition along with several destroyed street lampposts, fire hydrants, and a destroyed elevator door from one of the World Trade Center towers.
The exhibition includes pieces of the airplanes that crashed into the WTC. The details of the crashes are shown through graphics and brought to stark reality by a portion of the wheel assembly from one of the planes, a piece of fuselage, and a steel beam with an embedded airplane piece.
Source (Snapshots from panorama view mine, so pray I'm right)


Overview of both:

From National Geographic, also from the NY State Museum:
This fragment from one of the airplanes that struck the World Trade Center in 2001 was recovered in lower Manhattan. (Courtesy New York State Museum)
SourceA window frame of a B-767 that was recovered from the WTC wreckage. Notice the rivets in the lower portion of the window frame and the hi-shear hilocks surrounding the frame. Proof, the aircraft was a B-767 and the photo and videos depict an intact B-767, so once again, proof that the aircraft remained in one piece just before it struck the WTC building.
Source(I suspect that this is our beloved Beachnut talking under another alias)