Well, of the group you've got in there, Dunn's the obvious one out if you want to keep the HR/SB possibility open. All the others steal bases to some extent (though Berkman hasn't been running this year, as of yet).
Tonight, Dunn faces the Big Unit, who he's got a terrible history against, so that's all the more reason to sit him for this evening. Berkman is facing Marquis, who he's hitting over .500 against in his lifetime, for comparison.
For the long term, I recommend trying to move Dunn for another multi-cat player, possibly a 2B or SS. With Pena, Cabrera, and Berkman, your HRs look to be pretty covered from here on out with the additional numbers from Holliday and Hunter/Ordonez (assuming you switch them in and out when their respective streaks occur). Look for a team suffering from a power shortage and see if you can move them Dunn for a speedy 2B/SS (maybe even include another OF like Maggs and upgrade your 2B to an elite player).