Kyle Lohse has made 40 2nd half starts for the Cardinals and Brewers since the 2011 season, and owns a 19-6 record with a 3.10 ERA over 244.1 IP with 178 strikeouts. He is not going to dominate in the K category, but between QS, ERA & WHIP, Lohse is one guy to target for a post All-Star game run.
R.A. Dickey hasn't been great this year 6-7 with a 4.24 ERA, but over the last 3 season, after the All-Star game, Dickey has won 18 games for the New York Mets and Toronto Blue Jays, with 248 Ks over 302.2 IP.
Dan Haren has been a nice signing for the Los Angeles Dodgers, winning 8 games and owns an ERA under 3.60 with a 1.21 WHIP. Over the last 3 season, pitching for the Los Angeles Angels and the Washington Nationals, after the All-Star game, Haren has won 18 games (6 in each season) with a 3.71 ERA with 201 strikeouts in 252.2 innings pitched.
Ervin Santana had a rough month of May, but pitched 4 of 5 quality starts in June. Over the past three 2nd halves of the MLB season, Santana has tallied 16 wins for the Angels and Kansas City Royals. Actually, 16 of his 29 wins over the last 3 seasons have come post All-Star break.
Matt Cain owns a 2.70 ERA over 40 starts after All-Star games since 2011. This season hasn't been great for Cain, 1-6 with a 4.38 ERA, but his history proves he could be valuable in the 2nd half.