According to Jon Heyman, left-handed reliever Mike Gonzalez is starting to draw some interest. Gonzalez has a history of arm problems, and underwent knee surgery in October. He rejected a non-roster invitation from the Texas Rangers in March.
A team with the need and motivation to sign a lefty is the Boston Red Sox. So far the Red Sox are only "monitoring" the market for Gonzalez. The only current left-handed reliever on the Red Sox roster is Andrew Miller, who could shift to the rotation sometime during the season. Gonzalez owns a 10.3 K/9 for his career, second among active left-handers.
The Cleveland Indians reportedly had interest in Gonzalez, however they recently acquired Rick VandenHurk, signaling they may want to go a cheaper rout in building their bullpen. While the Indians haven't completely pulled out of the running for Gonzalez, VandenHurk's singing suggests they will not be aggressive.
Gonzalez is one of the most attractive free agents left on the market. While a reliever coming off knee surgery doesn't sound exciting, having a left-handed specialist capable of getting high-leverage outs has been essential to recent World Series winners. Just ask the Texas Rangers about facing Arthur Rhodes, Marc Rzepczynski and Javier Lopez. On second thought, don't ask.