I am usually not in favor of retiring players' numbers after that player has left your team, and is currently playing for another team. For instance, I think the Sixers should wait to retire Iverson's number when he finally ends his illustrious career. You have to look at basketball numbers differently since you only have 12 players on your roster, and therefore it is much easier for management to prohibit a player from using number 3.
The Philadelphia Eagles are the self-proclaimed "gold standard" of the NFL. Go back about two months, and the Eagles took a huge public relations hit with the way they handled the Dawkins debacle. They basically slammed the door shut on a fan favorite, the best player to put on an Eagles uniform since Reggie White, and maybe the most loved of all-time. The Eagles as an organization did not want Dawkins' diminishing skill to be exposed out on the field, and thus chose not to resign him. Admittedly, Dawkins has lost a step, and was not the same defender he was in his prime in one on one coverage situations against an opposing wide receiver or tight end. Dawkins was still a beast at stopping the run and leading the defense to its greatness. He single-handedly forced two fumbles in the first half which blew the game open in the Eagles destruction of the Cowboys the final weekend of the season. Either way, no matter how the Eagles handled the situation of not resigning Dawkins and letting him sign elsewhere, they were going to come out looking bad. However, the way the organization handled the situation was nowhere close to the "gold standard" that they claim to be.
Brian Dawkins and the Denver Broncos come to Philadelphia on December 27th. This game will be emotional for everyone involved; the fans, the Eagles, and especially Dawkins. The Eagles should have a pre-game ceremony honoring Dawkins and retiring his number 20 into the Eagles Honor Roll. Dawkins will be done playing in a year or two and you want to rebuild the bridge that the Eagles organization burned so quickly this summer. He will be a great ambassador to the community, and for the team in general. This will also help to improve the Eagles recent image of not caring for their players. I also hope that this will keep Dawkins involved in Eagles football in some way, possibly by joining the coaching staff. Whatever happens with Dawkins after his career, the Eagles should feel obligated to honor Dawkins when he comes to Philadelphia late this season.