I expect Bruney, Batista, and Tavares to open up a few spots, and Walker may do so as well. Of course, those three could be Wang, Detwiler and Zimmermann, but I think we'll see some moves in mid to late July that open up a spot or two.
Walker is solid and durable. Batista is very useful as an arm that can be pitched into oblivion if needed, and his numbers have been reasonable for a garbage time specialist.
Bruney is a very talented pitcher slumping.
Tavares is a AAA player. Seems like a cool guy, but his play says DFA.
