Norman Coinage
The coins of the Norman period (1066-1154) are often highly prized finds by metal detectorists, and some people may go their entire detecting career without ever finding even a fragment of a Norman coin. However, the limited numbers and types of these coins means they aren't the hardest of all the hammered coins to identify. This is because each type (up until Stephen that is) has a slightly different obverse and reverse.
A copy of Coins of England and the United Kingdom is a very useful book in helping with identifying your Norman coin.
A very good website already exists discussing in depth the coins from William I to Stephen and the Anarchy. The types listed can easily be referenced with Spink.
The coins of William I – Henry I can be found here:
http://www.symbolicmessengers.com/Norman_Coins_of_England.htm
The coins of Stephen and the Anarchy can be found here:
http://www.symbolicmessengers.com/Coins_of_the_Anarchy.htm
The Early Medieval Corpus is also a great database to help you find similar examples of your coin.