.930+ OPS, 100-6000 PA in career (since 1900)
1.013 OPS, 198 PA Brennan Boesch (2010)
.952, 3445 Ryan Howard (2005-2010)
.945, 3659 Lefty O'Doul (1919-1934)
.940, 5556 Hack Wilson (1923-1934)
.940, 5690 "Shoeless" Joe Jackson (1908-1920)
.931, 4736 Miguel Cabrera (2003-2010)
.931, 1518 Joey Votto (2007-2010)
.930, 151 Jack Cummings (1926-1929)
The four active players on the list are interesting and difficult to predict. Miguel Cabrera, who has already had a great career, and appears to be hitting his stride. He's only 27 and should walk away with at least a few MVP awards and a ticket to the Hall when he retires someday. His OPS this year is 1.031, and his it will probably go way up over the next few years as he punished AL pitching.
Ryan Howard is signed with the Phillies through 2016 at around $25 million a year, so he needs to have a great OPS into his mid-30's (even if most of baseball history suggests that won't happen). His OPS this year is only .857, and a big part of that is that he doesn't walk nearly as much as he used to (20 BB in 300 PA this year vs. 107 BB in 648 PA in 2007). Maybe he's less patient or less feared, but either way it's a bad sign. If he finishes with a .300 BA and over 140 RBI this year, though, the Phillies will probably be pleased.
Joey Votto is having another productive season (.961 OPS, 15 HR, 47 RBI). He might never become a huge star like Miguel Cabrera, but he is putting up impressive numbers all around, including with walks this year (9th in the NL).
Brennan Boesch has had an amazing first couple of months to his career, winning the AL Rookie of the Month in May. It's too soon to know what kind of player he's going to become, although there haven't been any big problems yet. Some players that start strong just keep on going with it (Ryan Braun, Albert Pujols), but most have a letdown even if they become solid contributors (remember Garrett Jones' great start last year?). It's too early to tell with Boesch, but he's given the Tigers a jolt and he might have a spot in their outfield for a long time.