After André's execution, George III ordered a monument to be erected for him in Westminster Abbey. Its main text reads:
 

Sacred to the memory
of
MAJOR JOHN ANDRE,
who, raised by his Merit, at an early Period of his Life, to the Rank of
Adjutant-General of the British Forces In America,
and, employed in an important but hazardous Enterprise,
Fell a Sacrifice to his Zeal for his King and Country,
on the 2nd of October, 1780, aged 29,
Universally beloved and esteemed by the Army
in which he served, and lamented even
by his Foes.
His gracious Sovereign
King George III.
has caused this Monument to be erected.

John's body was exhumed in the summer of 1821 and transported back to England, where he was reinterred within Westminster. At that time, a second inscription was cut into the base of the monument:

The remains of Major JOHN ANDRE were, on the 10th of August, 1821, removed from Tappaan by JAMES BUCHANAN, Esq., his Majesty's Consul at New York, under instructions from his Royal Highness the DUKE OF YORK, and, with the permission of the Dean and Chapter, finally deposited in a grave contiguous to this monument on the 28th of November, 1825.

Photography isn't allowed within the Abbey, but when I visited there on a recent vacation to the UK, a verger was kind enough to give me permission to take the accompanying photo. He even pointed out the exact location of the "grave contiguous to this monument."

A couple of different monuments have marked the place in New York where John was hanged and originally buried. I took some photos of the site on a visit in June 2003, and Doc M has an article about them on her funerary page at The Silver Whistle [see links].