Great graph from NY Times on the correlation between payroll and wins in MLB over the last decade. NFL and NBA are capped, but baseball is not (click on the pic for a more glorious image).
Biggest overachievers are Oakland and Minnesota, biggest underachiever (in terms of vertical distance from the regression line is Baltimore.
My two teams are the Tigers and the Cardinals. Pretty big difference in bang for buck between them. Cards are spending just north of $100 million for just north of 90 wins while Tigers are just south of $100 million for just south of 75 wins.
Mets and Cubs are the worst performing big spenders.