DE Luis Castillo (re-signed, 1 Year) -- This is the best value of all the signings. Even if Castillo does not win back his starting job, he figures to play as many snaps as Vaughn Martin and Corey Liuget. He is not the disruptive force he once was, but he still anchors against the run and keeps offensive linemen away from his linebackers.
WR Roscoe Parrish (via Buffalo, 1 Year) -- Fantasy footballers can consider Parrish a handcuff for Eddie Royal. While Parrish provides injury insurance and depth at a slot receiver position that will take on more importance in 2012, he will not see a lot of playing time if the receivers ahead of him stay healthy.
NT Antonio Garay (re-signed, 2 Years) -- Of all the "second wave" signings, this one is the most important. Garay is not a prototypical 3-4 nose tackle, but he is a disruptive force in the middle who can collapse the pocket and make plays in the backfield. With the fast-improving Cam Thomas there to spell him, Garay is in for a big season.
TE Dante Rosario (via Denver, 1 Year) -- There are three talented tight ends in front of him, but Rosario is good enough to win a spot and carve out a niche in the offense. He is a reliable route runner who fights for the ball and makes tough catches. If Antonio Gates' foot issues return, this signing will take on added importance.
TE Randy McMichael
QB Charlie Whitehurst (via Seattle, 2 Years) -- The change from Billy Volek to Whitehurst was financially motivated, but A.J. Smith values depth at the QB position, which means he trusts Whitehurst. The Chargers spent four years developing Whitehurst and now he has big-game experience, to boot.
SS Atari Bigby (via Seattle, 2 Years) -- This pickup does not plug the hole at strong safety that has lingered since Rodney Harrison's departure. But Bigby is an upgrade over Steve Gregory and can make plays when pressed into duty; in the two seasons he started more than six games, he averaged 4.5 INTs.
WR Eddie Royal (via Denver, 3 Years) -- Royal fills two bigs needs: slot receiver and punt returner. As a receiver, he will be a go-to target on third downs and help open up the middle for Gates. As a returner, he represents a massive upgrade over Patrick Crayton. Last season, Royal averaged 16.2 yards per punt return, compared to 9.2 for Crayton.
TE Kory Sperry (re-signed, 1 Year) -- This signing went largely unnoticed, as Sperry has caught just five passes in his two years with the Chargers. But two of those passes went for more than 30 yards, showing his big-play ability. More importantly, he has made huge strides in terms of blocking prowess and overall technique.
FB Le'Ron McClain (via Kansas City, 3 Years) -- Ryan Mathews had a Pro Bowl season in 2011. As a reward, the Chargers gave him a road-grading fullback who will help him get back to Hawaii. McClain is the kind of dominant lead back the Chargers have lacked since Lorenzo Neal left town. He can also tote the ball with authority, which will help offset the loss of Mike Tolbert.
OLB Jarret Johnson
LT Jared Gaither (re-signed, 4 Years) -- The Chargers took a chance when they released Marcus McNeill without having Gaither locked up, but the gamble eventually paid off. Gaither did not allow a sack in five starts after being claimed off waivers and stabilized the entire offensive line. The key for him is maintaining that high level of play now that he is no longer playing for a contract.
WR Robert Meachem (via New Orleans, 4 Years) -- As far as Plan B's go, Meachem is a pretty good one. San Diego quickly inked Meachem after losing the bidding war for Vincent Jackson. Meachem becomes Rivers' new downfield threat and owns one of the highest catch-per-attempt rates in the league. He is no V-Jack, but he has 70-catch, 1,100-yard potential.
C Nick Hardwick (re-signed, 3 Years) -- The offensive line was priority 1A this offseason, so retaining the captain of that unit was vital. Hardwick entered the league with Rivers in 2004 and the two have a great working relationship. The Purdue product will also make life easier for Tyronne Green, who is expected to replace the retired Kris Dielman as Hardwick's left-side wingman.
ILB Demorrio Williams (via Kansas City, 1 Year) -- Williams joined the Chargers before free agency officially opened, signaling San Diego's aggressive intentions. He replaces Na'il Diggs and will play mostly on passing downs and on special teams. He still has good speed but is not quite the playmaker he was earlier in his career.
Michael Lombardo is a long-time contributor to the Scout.com network. His analysis has been published by the NFL Network, Fox Sports and MySpace Sports. He has followed the Chargers for more than 16 years and covered the team since 2003. You can see more of his updates by following him on twitter.