Your have several offensive players who should have strong second halfs. Huff is traditionally a second half player. He bats thirty points higher in the second half for his career. I also see Teixeira's power coming around in the second half.
On the pitching side, I think you're in even better shape. I look for Pettite to have a great second half. With his good friend Clemens around, he should be resurgent.
I would say sell high on Liriano, but you're in a keeper league you deffinately can't. He should still finish with around 18 wins and a 3.00 ERA which still means some great numbers. If you in reach of first in your league, I'd look to trade him though. In a keeper league, the value you could get for him could help ou win the league. If you can, get a big bat for him. Win now, worry about next year later.