IDK what kind of format your league is, but this is based on my general observation so it should help in most to all formats.
In order of who to drop first to last:
Phil Humber-Ozzie is going to a 6 man rotation. That means no 2-starts and it throws the pitchers out of rhythm. On the other hand, the extra rest could help.
Francisco Liriano-He's been too volatile all season. He has flashes of brilliance, but then he relapses-hard. It's tough to even spot-start him.
Bartolo Colon-Colon is the biggest surprise. Outside of a few rough starts, he's been pretty solid. It never hurts to have a team that can hit behind you as well.
Ervin Santana-He's looking like the Santana we know. It's a shame that his team doesn't always hit for him.
Scott Baker-He's a fantastic sleeper pick and having a career year. After today, it looks like he's right back where he left off before he got injured.