I don't know how big your league is, but that looks like an above average but not great team in a 10-team league to me.
Guys I'd consider trading:
C B. Molina (in a bad offense, likely to tail off a bit after quick start)
SS M. Young (likely to tail off a bit after quick start ... though it goes with out saying that Texas's offense much better than SF's)
OF M. Kemp (I'll disclaim that I've never been high on him, but if you share my low opinion of him and see his value rising, that makes him an obvious sell high)
P E. Volquez (Baker will pitch his arm off by the end of the year. He's your most valuable trade bait in this group so don't sell him cheap just because he's a good candidate to sell)
Things I'd want back:
In any trade of Molina or Young, you'd obviously need a starter at C or SS back in return. You don't NEED to move either, but you could upgrade there in the right deal.
Otherwise, I'd look for outfield help (I love Upton, and like Quentin and Pence, but both as more of #3 outfielders than #2s), a stronger closer to put next to Nathan, or some pitchers in line for big second halfs ... guys like Harang or Penny that can be bought low right now but have still shown they have some stuff left.
The type of deal would obviously depend who you're offering ... I wouldn't be giving Volquez for Harang or Penny straight up, obviously, for example.
Overall, I think your major positive is that you have quite a few guys who have underperformed have either been healthy or are healthy now, which puts them in position for a good 2nd half: Fielder, Cabrera, Sabathia, Lackey and maybe even Maine all fit that description to me.
I'd make a couple moves, but don't think you need to blow anything up. Patience will get you places with that lineup.