When one looks at free agency in the NFL, there's a LOT to look at historically.
Before the NFL draft was implemented in 1936, all players in the NFL were basically signed as free agents. Some were rookie free agents, and some were veteran free agents.
If one looks at the Green Bay Packers from that era, one can see a number of players from both genres. Curly Lambeau signed veteran free agents like C Jug Earp, E Lavvie Dilweg, T Cal Hubbard, B Johnny (Blood) McNally and G Mike Michalske. Hubbard, McNally and Michalske all later went into the Pro Football Hall of Fame.
Lambeau also signed rookie free agents before 1936. This list included T Cub Buck, B Verne Lewellen, QB Arnie Herber, B Clark Hinkle, B Buckets Goldenberg and E Don Hutson. Herber, Hinkle and Hutson also were inducted into the Pro Football Hall of Fame.
Once the draft started, you could still sign a free agent, but this was done via three ways. You could still sign a rookie free agent. You could also sign a player who was released by another team. Or, you could sign a player who played out his option (or played until the end of his contract with a team).
That is what TE Ron Kramer and FB Jim Taylor did. Both played out their contract in Green Bay and then signed with the Detroit Lions and the New Orleans Saints respectively. In both cases, the Packers received first-round draft picks as compensation for the players leaving.
Up until 1989, these were the only means a player could sign with a new team. But in 1989, the NFL had a limited free agency called Plan B free agency. Plan B allowed all NFL teams to preserve limited rights of no more than 37 players on each roster.
Plan B allowed teams to match an offer for a player, if a player was deemed a Plan B free agent. The players that were unprotected were free to sign another team. However in 1992, a jury found that Plan B free agency violated antitrust laws, and that form of free agency was abolished.
Unrestricted free agency, or the form of free agency that is currently in place in the NFL, came into being in 1993. DE Reggie White was the poster child of that first unrestricted free-agent class. More on him later.
Regarding the 10 best free-agent signings in the history of the Packers, I'm going to go back to 1958 (the year before Vince Lombardi arrived in Green Bay and the year after Lambeau Field was built) as far as putting together this list.
This list will include players who were unrestricted free agents, "street" free agents or players who were released by their previous team and also rookie free agents. All but two of my top-10 players played on at least one championship team in Green Bay.
It's no wonder who I have heading the top 10.