My favorite undrafted rookie free agent is Noel Grigsby out of San Jose State. Some people like Mike Davis, but Grigsby catches everything and runs great routes. I'm not sure Davis is an upgrade over Denarius Moore in both the mental and physical departments.
Another guy I believe might have a chance to make the 53 is Denico Autry out of Mississippi State who seemed to be playing in the wrong system after being the best junior college DE in the country and had offers to go to any major program.
If George Atkinson III can show his wheels on kick returns in the preseason, it's likely Reggie could decide to keep him on the 53 in that role. If not, then Reggie will hope to get him to the practice squad.
Otherwise, I think every other player will be given a chance to succeed in the preseason and the best 8-10 will be exposed to waivers in hopes of landing 8 of them on the practice squad.