I have 34 rated as potential major leaguers. This doesn't mean they will all have the opportunity, but they could not make total asses of themselves.
I have one player rated as a potentail all time great, although he may not stay at C. That would be Jesus Montero.
I have 8 that could be superstar level players. Buster Posey and Carlos Santana are in this and at the low end of this is Kyle Skipworth. He may not get past AA, but the Joe Mauer comparisons out of high school will keep him on my radar for a couple more seasons, though his ceiling could drop or his floor could increase.
35 more could be solid starters. These are highlighted by Wilson Ramos and Tony Sanchez and range down to Omar Narvaez and Jorge Alfaro. Some of these guys have floors of middle level minor leaguers, though. This means they could never get passed high a ball, but they do have that possibility.
A couple of players that project to be a starter on some teams that I like are Carlos Ramirez and Lou Marson. One guy I like who is low on this list, at 57 actually is John Hester. He could be a very solid backup and occasional starter for a long time.