The Green Bay Packers aren't signing any undrafted free agents as long as the lockout remains in place. But they'll have their shot whenever free agency begins, and there were some good players left undrafted.
In 2010, the Packers didn't draft anyone to return kicks or play linebacker, so it wasn't a surprise when they targeted players who could fill those roles. They signed CB Sam Shields, who turned out to be a much better cornerback than kick returner (too many fumbles), and signed a couple college defensive ends to convert to outside linebacker, such as LB Frank Zombo.
But with so many draft choices in 2011 (10 players drafted) there aren't as many roster spots that will need additional depth. Still, Mocking The Draft has the list of the Top 25 undrafted players, and the Packers might be able to find a couple players with potential.
USC C Kristofer O'Dowd. It's surprising to see him available after NFL Draft Scout rated him as the 3rd best center and one of the Top 120 players in the draft. He's everything you could want in a center, except he had multiple injuries in college, and they were probably the reason he went undrafted. There are a couple other centers listed among the Top 25 available too. I mention the position for the Packers because they could have an opening behind C Scott Wells if Jason Spitz leaves in free agency. Even then, they'd still have Evan Dietrich-Smith and promising second year player Nick McDonald, so it's not a desperate need.
Delaware QB Pat Devlin. While a couple of similarly ranked players like Alabama's Greg McElroy and North Carolina's T.J. Yates were drafted, Devlin is still looking for a chance. It wouldn't hurt the Packers to bring a training camp quarterback as an extra arm anyway, but if the Packers do trade Matt Flynn then they'll need at least a new practice squad quarterback.
UCLA K Kai Forbath. I'm not desperate to see K Mason Crosby run out of town, but he could be a free agent, and he's far from the best kicker. Leg strength on kickoffs aren't as important with the new kickoff rules, but he hasn't been the most accurate kicker either. I wouldn't expect Forbath to beat him out, but I'd welcome the competition. And he was rated as the No. 2 kicker in the draft by NFL Draft Scout.