I have been doing my family genealogy for a few years on and off and have come across a reference in my family history of the last name "Preston" or "Prestun" in Knights Templar documents. I have come across this statement or similar a few times.....
" The first recorded spelling of this surname of Preston was shown in the Records of the Knight Templars in 12th Century England. Peter de Prestun was recorded in the year 1185 as the first spelling of the name. "
Is there any known great websites where I can do some Templar research?
Malcolm Barber's book and his collection of the translated primary sources on the Templars, The Templars : Selected sources (co-edited with K. Bate), Manchester: Manchester UP, 2002 are usually good introductory books, but OP's case might be a bit special.
OP stated above that the document in question is dated to 1185, but such kind of documentary sources, like the record of land transactions, are not necessarily translated from Latin into modern English.
I assume that OP's the document in 1185 that alludes to "Prestum" is probably the inventory document of the order and its property in 1185, and it was at least published with commentary in 1935, as Beatrice A. Lees (ed.), Records of the Templars in England in the twelfth century : the Inquest of 1185, with illustrative charters and documents, Oxford: OUP, 1935, rep. 1991, but I'm afraid the full text is only available in Latin (though checking the proper name in Latin is easier to understand the whole document). Neither I know this primary text is available for free somewhere on online (many of them in online edition require the authorization via academic institutions).