Check here: http://coppercoins.com/diesearch.php Looks like maybe could be 1951D-1MM-006 based on your pictures. But hard for me to tell for sure.
There are over 39 rpm's for the 51 D Lincoln cent that said go to varietyvista.com and have fun sorting through the lot.
Theres only one thing that I would like to add, each site is good for reference, I like http://varietyvista.com/index.htm because it is published by Coneca, Coneca has been the authority for die variety's since 83'. In fact the organization was started in 1956. I say, to each his own. I have found that Variety Vista is the easiest to navigate. Each site will give you photos of the same variety Also, the photos are sometimes taken from a different view and lighting and that can be extremely helpful.