Christian Yelich and Jake Marisnick were called up by the Marlins. Yelich is worth a pickup in all formats and should be a top-40 outfielder the rest of the way. You can read more about them here http://www.faketeams.com/2013/7/23/4548640/marlins-call-ups-christian-yelich-and-jake-marisnick
Jenrry Mejia will start against the Nationals tomorrow night but will likely be sent back down afterwards. If you are streaming in an NL-only league then he's an interesting option. He has a 2.55 ERA over 6 minor league starts thus far this season. There obviously a chance he could replace Jeremy Hefner in the rotation should Hefner continue to struggle.
Tim Hudson broke his ankle and will miss the rest of the reason.
Matt Holliday will likely return when he's first eligible this Saturday.
Chris Carpenter has been shut down and things don't look good for this return. I was excited for the potential impact he could make if healthy but this was always a risky situation.
Matt Kemp will miss a couple weeks with an ankle injury. This year has been an utter disaster for him and many of his fantasy owners.
Dominic Brown will be out about a week with concussion-related symptoms.
Jason Grilli was placed on the DL with a forearm injury. It's not known exactly how long he will be out but he has a chance to return in about 3 weeks if the injury is deemed to be minor.
Ryan Braun was suspended for the rest of the season due to PED-related issues.
Junior Lake has been red-hot at the plate and is now worth a pickup in all formats. He's eligible at SS, MI, and OF in some leagues. It's questionable as to how much of a consistent impact he will have over the next couple months but right now he's hitting for average and power while he has unquestionable stolen base potential.
Brian Wilson could be pitching in the majors within the next few weeks and there is a chance he could close wherever he signs. More likely than not he will pitch in a setup role though.
Carlos Torres has pitched well in the starting rotation for the Mets. He's someone to take a flier on in NL-only leagues.