As I wrote a few weeks ago, the Packers were in a sort of odd Free Agency position, in which they obviously had a good thing going and would probably seek to keep the gang together. That said, there are some serious needs on the team, which, well, they need to address if they want to have the same level of success going forward. (And hint: they won't. 15-1 records simply are not sustainable).
For the most part, the Packers did a good job of keeping the team intact. Mainly, it was all about Jermichael Finley. Everybody knew that Matt Flynn was gone. But, Finley was the guy to keep around. He is a big part of their offense, and should be a huge help going forward these next two years.
The only really big loss on the Free Agent side of things was C Scott Wells. Now it's not like their OL was a strong suit last year, so the Packers are hoping that Jeff Saturday will be an upgrade. That being said, I would expect them to take a look at using their 756 draft picks (reality compels me to tell you that they only have 12 picks. Yeah. 12. Only 12. That's it.) on an o-lineman. Some people have been estimating that Peter Konz could still be on the board for the Packers at pick 28.
Flipping to the d-line (or even LBs), the Packers really need to shore up their pass rush. Clay Matthews can have all the awesome hair he damn well pleases, but until teams stop double teaming the L'Oreal out of him, he ain't going to sack many QBs. Managing an upgrade with one of those 12 (!!) picks would go a long way with helping...
...the other team need: the Secondary. While maybe not as big of a need as pass rush, I don't think that the Packers can count on super human Aaron Rodgers to show up every game.