The following have consistently underperformed for me. I know others swear by some of them, but I swear at them.
C `61 Elston Howard, `35 Jimmie Foxx (the `59 Howard for $3M is a steal)
1B Lou Gehrig (pains me to say it), Albert Pujols (all seasons), Norm Cash `61 (beyond awful), Darin Erstad `00 (worse than Cash)
2B Joe Morgan (well chronicled in SIM)
SS Troy Tulowitzki, Ernie Banks (putrid)
3B Joe Torre `71 (as noted elsewhere), Al Rosen `53 (absurdly overpriced)
OF Willie Mays, Mike Trout, Reggie Jackson, George Foster
SP Ed Walsh `10 (100 fewer IP and more expensive than Ed Walsh `08, always underperforms him -- always), Claude Hendrix `14,
Bob Gibson `68 (hurts me to say it), Vida Blue `71, Catfish Hunter `72, Lady Baldwin `85 ,Babe Adams `09 (bust as a starter or long reliever)
RP Eckersley `89 and `90 (broken), Mariano Rivera (nearly all seasons), Melancon, Jake McGee, Wade Davis