Jon Paul Morosi of FOXSports.com lists his predictions of trade candidates:

Luke Gregerson, RHP, San Diego Padres: The reliever could go to the Phillies who are short on late inning relief.
Jason Frasor, RHP, Toronto Blue Jays: The Cubs and Angels could benefit from the right-hander.
Scott Downs, LHP, Toronto Blue Jays: The pending free-agent could fit the Mets since the team is short on setup men.
Augie Ojeda, 2B/SS/3B, Arizona Diamondbacks: The Red Sox are short on infield reserves and Dustin Pedroia injured his left wrist on Tuesday night.
Omir Santos, C, New York Mets: He’s at least third on the depth chart in New York and the Dodgers are in need of an experienced catcher.
Heath Bell, RHP, San Diego Padres: San Diego is rebuilding and the Twins are gunning for a championship.
Sean Burnett, LHP, Washington Nationals: Burnett could be the best option to replace J.P. Howell.
Manny Parra, LHP, Milwaukee Brewers: The Brewers have a surplus of pitchers and the Diamondbacks need starting pitching depth nor do they have a left-handed starter.
Brandon McCarthy, RHP, Texas Rangers: The pitcher does not have a clear role with the Rangers. He could be a candidate for the Washington Nationals.
Mike Lowell, 3B/1B, Boston Red Sox: The Rangers could use a veteran bat, but he has a high price tag of $12 million owed to him this season.