What was the name of Paul Revere's horse?

No one knows. Many names have been suggested over the years, but there is no historical record to verify any of them. What is known is that Paul Revere rode a horse provided by Deacon John Larkin. No contemporary Larkin family records give a name for the horse. The naming of horses was not common at the time.

I have found these sites that say it was 'Brown Beauty':

(old links all dead. see below for updated link(s) )

We can't be 100% sure. What we do know though is that the only name with any actual historical evidence is Brown Beauty for Paul Revere's horse.

This seems pretty definitive, and from the society that handles his historical house:

Revere left several accounts of his ride, and although he states that he borrowed the horse from John Larkin, neither he nor anyone else takes much notice of the mount, or refers to it by name. Revere calls it simply "a very good horse." In the years since 1775 many names have been attached to the animal, the most exotic probably being Scheherazade. The only name for which there is any evidence, however, is Brown Beauty.

The following excerpt is taken from a genealogy of the Larkin family, published in 1930.

"Samuel (Larkin) ... born Oct. 22, 1701; died Oct. 8, 1784, aged 83; he was a chairmaker, then a fisherman and had horses and a stable. He was the owner of "Brown Beauty," the mare of Paul Revere's Ride made famous by the Longfellow poem. The mare was loaned at the request of Samuel's son, deacon John Larkin, and was never returned to the owner."

According to this source, the famous horse was owned not by Deacon John, but by his father - if true, this would mean that not only did Revere ride a borrowed horse, but a borrowed, borrowed horse. That it had a name is difficult to prove in the absence of corroborating evidence.

https://www.paulreverehouse.org/bio/faq.html

Samuel (Larkin) ... born Oct. 22, 1701; died Oct. 8, 1784, aged 83; he was a chairmaker, then a fisherman and had horses and a stable. He was the owner of "Brown Beauty," the mare of Paul Revere's Ride made famous by the Longfellow poem. The mare was loaned at the request of Samuel's son, deacon John Larkin, and was never returned to the owner.

Mounted on Brown Beauty, one of the swiftest horses in Massachusetts, Paul Revere warns his fellow patriots of the arrival of the British regulars.

http://www.pbs.org/wnet/historyofus/web01/features/see_it_now/1770.0111.html
http://www.paulreverehouse.org/bio/faq.shtml

This seems pretty definitive, and from the society that handles his historical house:

"The only name for which there is any evidence, however, is Brown Beauty."

https://www.paulreverehouse.org/bio/faq.html