I'll go position by position.
Sal Perez - KC - the guy can hit, nice deep sleeper.
Jonathan Lucroy - this guy should be ready come off the DL early in the second half and was mashing before. For a good bit of the first half he was the best catcher and can easily do that again he did it last year as well.
Michael McKenry - so long as he's swinging the bat well he only has to fight off an injured/aging Rod Barajas for playing time.
Yasmani Grandal - good young catcher will have nothing to lose after Hundley was demoted. The position is his for the running
JP Arrencibia - good power numbers for your catcher slot, though the BA will suffer a bit.
Brett Wallace - now that Carlos Lee is done in Houston, they will probably bring up Wallace for an extended look. He has seemingly figured things out in AAA nad his power numbers are back. He probably won't ever hit for a good average but there is serious pop in his bat and he could put Adam Laroche like numbers if he's brought up and given a chance again.
Ike Davis - Some may have given up on him for this season but he is on pace for 25 homers and 100 RBI and that's solid production from your 1b/CI slot in deeper leagues and his BA can only get better.
Adam Laroche - His numbers are right where they normally are, maybe a tick more RBI than we're accustomed too, but his second half studly runs? BUY BUY BUY if you can.
Mark Teixeira -- Like the above his peripheral stats are ok and he's starting to turn the corner if you haven't noticed! Buy low
Justin Morneau - Yeah seriously, he's finally healthy for an extended time and finally showing signs of his former self buy very low and you might be rewarded with studly second half numbers, especially if he gets dealt to a contending team. Would be just what the doctor ordered. Baltimore could use him and move Reynolds to bench or platoon DH.
Adam Lind - go get him if you need a 2nd inf/CI/utl bat in deeper leagues and especially if you need some cheap power.
Chris Getz - Will return from his injury shortly after the ASB and could be a nice deep sleeper MI for some cheap speed in the second half.
Rickie Weeks - I know he's been a disappointment but he's shown recent signs of life and well he can't get any worse. You could take a flier here.
Chase Utley - He's been hurt any kind of production he can give will be boost
Ben Zobrist/Dan Uggla - the power numbers have been there, but the BA will come around in the second half buy very low if you can.
Casey McGahee - He is starting for Pittsburgh and has started to show some signs of life in his bat not bad for a deep league sleeper.
Ryan Zimmerman - Buy low if you still can!
Hanley Ramirez - He's been quietly solid and the BA will be on the rise in the second half. Buy low if you can.
Evan Longoria - Sure you'll only get him for a month or so but its worth it for the stretch run (stretch run sleeper alert)
Emilio Bonafacio -- Starting 2nd half he'll be off and running, you should swoop in and get him if he's available for cheap!
Shane Victorino - HIs BA isn't where it normally is but he'll improve and he does have 19 SB so his speed hasn't faltered despite his lower BA. Utley is back and Howard is right there waiting so his lineup protection is there. If he's traded he might get dealt to an even better situation which would be good for him.
Shin Shoo-Choo - Solid power numbers, might can get him somewhat cheaper than you normally could. Be a ncie OF-3 if you have studs like Jones, Beltran, Reddick, Bourn, Braun, etc clogging up your other spots.
Jay Bruce - if you need power go get em. He's a feast-or-famine type of player but you can't ignore his power and I think he'll improve when things get crucial.