I don't know about the All-Star Break, but I would be surprised if Posada, Hunter, Youkilis, Lowell, and Upton end the season in the top ten in OPS in the AL. In the NL, I would only be surprised if Hardy finished in the top ten. However, I'm going to predict that Griffey either won't qualify (due to an injury) or will falter down the stretch.

As to the pitching side of the ledger, I'll go on record and say that Meche, Carmona, Kennedy, Gorzelanny, Lowry, (Shawn) Hill, Bergmann, and Marquis will not rank in the top ten in ERA in their respective leagues. If any of them make it, I'll bet it's because ERA isn't necessarily the best indicator of pitching performance.

As for hitters and pitchers who will work their way into the top tens, I'll make those predictions in a subsequent comment.

i agree that posada is due for a fall. his PrOPS is only .847. i also nominate pettitte to drop off the list. his FIP is a full run higher than his ERA.

My best guesses:
Al OPS
Falling Off:
Posada, Youkilis, Lowell, Hunter
Joining:
Hafner, Manny Ramirez, Giambi, Morneau

AL ERA
Falling Off:
Meche, Carmona, Beckett, Kennedy, Pettite, Shields
Joining:
Johan Santana, Halladay, Matsuzaka, Felix Hernandez, Jeremy Bonderman, Erik Bedard

NL OPS(hardest one to pick)
Falling Off:
Derrek Lee(highest BABIP in the NL), Chipper Jones (HR/FB is high), Hanley Ramirez
Joining :
Albert Pujols (BABIP is very low), Carlos Beltran, Lance Berkman

NL ERA
Falling Off: (I wouldnt be suprised if Peavy is the only one leff)
Ted Lilly, Noah Lowry, Shawn Hill, Jason Bergman, Jason Marquis, Brad Penny
Joining:
Matt Cain, Aaron Harang, Cole Hamels, John Smoltz, Roy Oswalt, Tim Lincecum

Completing my predictions, I will say that Hafner, Morneau, Teixeira, and Sizemore replace the players I mentioned above (Posada, Hunter, Youkilis, Lowell, and Upton) in the AL's top ten in OPS. Over in the NL, I'll go with Pujols and Berkman as replacements for Griffey and Hardy. Beltran, A. Ramirez, and Utley will either be in the top ten or not too far back.

As for ERA, I'll go with Santana, Bedard, Hernandez, and Sabathia to unseat Meche, Carmona, Kennedy, and Pettitte in the AL; and Hamels, Oswalt, Smoltz, Lincecum, and Sheets to replace Gorzelanny, Lowry, (Shawn) Hill, Bergmann, and Marquis. Webb will be in the mix, too.

AL OPS Falling Out: Torii Hunter, Kevin Youkilis, Derek Jeter, Mike Lowell.

AL OPS Climbing Up: Travis Hafner, Justin Morneau, Mark Texiera, Curtis Granderson.

AL ERA Falling Out: Fausto Carmona, Josh Beckett, Joe Kennedy, James Shields.

AL ERA Climbing Up: Johan Santana, Jered Weaver, Jeremy Guthrie.

NL OPS Falling Out(Toughest one): Todd Helton, JJ Hardy.

NL OPS Climbing Up: Aramis Ramirez, Carlos Beltran.

NL ERA Falling Out: Brad Penny, Ted Lilly, Shawn Hill, Jason Bergmann, Jason Marquis, Ian Snell.

NL ERA Climbing Up: Roy Oswalt, John Maine, John Smoltz, Oliver Perez, Rich Hill, Cole Hamels (This one's a reach, but I think he can do it).

(I apologize if this looks confused, I'm not sure if I'm formatting this correctly and the preview button seems to indicate I'm not).

Oops, CC Sabathia should also be included in the AL ERA Climbing Up.

As long as I am not asked to defend or even explain my choices:
AL OPS (Falling out): Hunter, Lowell, Upton
AL OPS (Climbing in): Hafner, Sizemore, Manny

NL OPS (Falling out): Hardy, Chipper
NL OPS (Climbing in): Pujols, Beltran

AL ERA (Falling out): Meche, Carmona, Kennedy, Pettitte
AL ERA (Climbing in): Santana, Matsuzaka, Kazmir, Sabathia

NL ERA (Falling out): Hudson, Penny, S. HIll, Bergmann, Marquis
NL ERA (Climbing in): Webb, Oswalt, R. Hill, Lincecum, Hamels

AL OPS drop outs:
Posada, Hunter, Lowell, Upton
Replacements:
Morneau, Hafner, Texiera, Victor Martinez

NL OPS dropouts:
Griffey Jr., Ramirez, Hardy
Replacements:
Beltran, Dunn, Burrell

AL ERA dropouts:
Lackey, Kennedy
Replacements:
Johan Santana, Chad Gaudin

NL ERA dropouts:
Lowry, Hill, Bergmann, Marquis
Replacements:
John Smoltz, Roy Oswalt, Cole Hamels, Ollie Perez (!)

Some wild guesses here, but what the heck, it's all in fun.

Out by ASB:
AL batters -
Upton, Lowell, Hunter

NL batters -
Hardey, Ramirez

AL pitchers -
Pettitte, Carmona, Kennedy

NL pitchers -
Marquis, Hill, Lowrey

In by ASB:
AL batters -
Swisher, Hafner, Teixiera

NL batters -
Beltran, Ramirez

AL pitchers -
Santana, Sabathia, Gaudin

NL pitchers -
Smoltz, Perez, Oswalt

Hitters:
Out in the AL: Posada, Youkilis, Upton and Lowell
In in the AL: Thome, Morneau, Hafner and Sizemore
Out in the NL: Helton, Griffey, Ramirez, Hardy
In in the NL: Beltran, Pujlos, Wright, Howard

Pitchers:
Out in the AL: Carmona, Beckett, Pettite and Shields
In in the AL: Santana, Hernandez, Sabathia and Dice-K
Out in the NL: Hudson, Hill, Marquis, Bergman, Snell
In in the NL: Webb, O. Perez, Sheets and Cain