Dan Haren, Dodgers: After a stellar April, Haren has lost four of his last six starts, and has seen his ERA balloon from 2.84 to 3.50 in the process. His strikeouts have taken a dive over that period as well. He has just 18 strikeouts in 37 innings pitched. That said, Haren has not had a real clunker in that span. He has given up four runs a few times, but never more than that. Still, his velocity is down, and the home runs are up. That has caution written all over it, and in standard leagues, you can probably do better.
Ervin Santana, Braves: Santana has given up three runs or more in all but one of his starts since April 25th. He has also walked at least one in every start this year except for one. Santana has been stuggling enough that you can do better in a standard league, especially those with start caps, which most have. Keep him and play matchups if you must, but his inconsistency makes it tough to do that as well.
Marco Estrada, Brewers: Much like Santana, he has given up three runs or more in seven of his last eight starts. He has also walked seven and hit a batter in his last two starts, so his command seems to be off as well. His numbers are not worthy of keeping around in standard leagues.
Jesse Chavez, Athletics: The fun part is over, folks. Chavez has come back to earth some, putting out just one quality start in his last four tries. He still has not given up more than four runs in a start, but he has been at that threshold three times out of his last six starts, so there is some cause for concern. There are safer options in standard leagues.