Surplus hardware
Two complete Saturn Vs went unused after the Apollo program, SA-514 and SA-515, as well as the third stage of the SA-513. SA-513 was the original launch vehicle destined for the Apollo 18 mission; it was used to launch Skylab (its third stage built from a converted S-IVB #212).
At the Johnson Space Center the Saturn V display is made up of the first stage of SA-514, the second stage from SA-515 and the third stage from SA-513. This display is made of real flight-worthy vehicles including an unflown command module (CSM-115).
At the Kennedy Space Center the Saturn V display is made up of S-IC-T (test stage) and the second and third stages from SA-514. The command module on display at KSC is a boilerplate, BP-30.
The first stage from SA-515 resides at the Michoud Assembly Facility, New Orleans, Louisiana and the third stage was converted for use as backup Skylab and is now on display at the National Air and Space Museum.
Likewise the canceled flights' CSMs and LMs went either unused or were used for other missions:
After Apollo 15's original H mission was canceled, there was a surplus H mission CSM and Lunar Module. CSM-111 was used for the Apollo-Soyuz Test Project. LM-9 is on display at the Kennedy Space Center (Apollo/Saturn V Center)
Apollo 18's CSM and LM were used by Apollo 17.
Apollo 19's CSM (#115) is displayed on the Saturn V located at the Johnson Space Center. Its LM (LM-13, originally assigned to Apollo 1 was only partially completed by Grumman and is now on display at the Cradle of Aviation Museum on Long Island. This LM was completed for the HBO miniseries From the Earth to the Moon for use as a prop in moon exploration scenes.
Apollo 20's CSM was never completed and was scrapped. The LM was also scrapped before completion, though there are some unconfirmed reports that some parts (in addition to parts from the LM test vehicle LTA-3) are included in the LM on display at the Franklin Institute, Philadelphia, Pennsylvania.