According to Marc Lancaster, the Rays would prefer to fill their need for a fourth outfielder via trade as opposed to signing a free agent such as Kenny Lofton.
Lancaster notes the Rays are likely to offer one of their surplus of starting pitchers. The Rays have five pitchers competing for the final two spots in the rotation and two of those pitchers (Edwin Jackson and Jason Hammel) are out of options. In addition Lancaster mentions that the Rays have a number of pitching prospects at AA and AAA that could be included in a deal.
The Rays would prefer a player that in addition to regular playing time in right field, can serve as a backup to center fielder BJ Upton. Lancaster lists several players that match this description including Juan Rivera, Reggie Willits, Coco Crisp, Reed Johnson and Ryan Freel. Ken Rosenthal previously said that Willits is untouchable, and Crisp and Johnson seem unlikely as trades rarely occur within a division. The Reds seem like the best fit of this group as they have been rumored to be active in the trade market this off-season for a starting pitcher.