Of those three, Calico would make the most sense, as he has the size (6-foot-4, 220 lbs.) and big-play ability the Chargers prefer at the position. He sat out the 2006 season after being cut in September, but at 26 years old he still has the potential to develop into a starting receiver.
Another position that could use an additional experienced body is cornerback. As it stands now, the Chargers are one injury away from Steve Gregory taking over as the nickel back. It would be prudent of Smith to sign a veteran dime back who can play the nickel if necessary. Available players who fit that description are Daylon McCutcheon, Will Poole and Chris Cash.
It is hard not to like what the experienced and classy McCutcheon brings to the table. During his eight years with the Cleveland Browns, he racked up 424 tackles and a dozen interceptions. He missed the 2006 season with a knee injury but, if healthy, he would make an excellent insurance policy.
The final spot in need of bolstering is the defensive line, where the undersized Ryon Bingham and a slew of former undrafted free agents fill out the rotation. To improve depth at this critical position, Smith could look at Junior Siavii, Carl Powell or former Charger Adrian Dingle.
Siavii is inarguably the most talented of that trio. He played his college ball at Oregon alongside Igor Olshansky and went one spot after Igor in the 2004 draft (No. 36 overall). He has the girth (6-foot-5, 330 lbs.) to spell Jamal Williams at nose tackle and the quickness to play some snaps at defensive end.
Smith would be wise sign one or more of the aforementioned players to one-year deals. Each signing would improve depth and would have no financial ramifications -- other than eating up some of this year's cap space that would otherwise go unused. These are the low-risk, high-reward deals that separate championship teams from mere contenders.