If the Yankees were to add one bat for the remainder of the 2014 season, a right fielder would make the most sense. Carlos Beltran hasn't been able to play in the outfield for months and Ichiro Suzuki has been absolutely anemic with the bat. Adding even a competent hitter there would be huge boon for the Yankees the rest of the way, like Chase Headley has been at third base. Brian Cashman has discussed the likes of Josh Willingham and Alex Rios, but someone that might make some sense is Marlon Byrd.
This year Byrd has hit .270/.318/.477 with 20 home runs, which is good for a 119 wRC+. He would automatically give the Yankees a much-needed power boost. Perhaps best of all, Byrd would provide the right-handed power they have been missing all season long. Unfortunately, Byrd is on the verge of turning 37 and provides questionable defense in the field. You'd essentially be trading in Ichiro's glove for more power, so which is better to have? Though in the least, the Yankees could have both and bring in Ichiro in the later innings.
The biggest hangup of all is probably that he's signed through 2015 at $8 million, which is certainly not terrible, but is probably not preferable for his age-38 season. The Yankees have seen enough old outfielders turn into mush to blindly agree to that. He also has another $8 million vesting option based on plate appearances that they likely don't even want to deal with. Unless the Yankees are planning to go after Nelson Cruz in the offseason, this may be their best chance to add a power-hitting outfielder, since they don't have any outfield prospects ready to join the team. Still, considering it's Ruben Amaro Jr. they have to deal with, it's understandable if they feel they don't want to give up a lot for him.