The Xpatriated Texan provides some additional insights on the incentives behind corruption. He considers the position of individuals who are entrusted with extensive power in their official role, but are not given much personal power (in the form of a high salary). This can be especially important in the case of old-fashioned graft, but I think it is less important with respect to the more subtle forms of corruption that I emphasized in my earlier post on How Power Corrupts.
Apparently, in New Jersey, a member of the legislature oversees the disbursement of billions of dollars, but has an income that is less than the median income of the state. Here in PA, the legislature gets a handsome compensation, so I didn't think that this was a problem for them. However, I've long thought that this disparity was important when it comes to the officials who actually implement the law--such as the cops. Here in Pittsburgh, I've gotten the impression that cops can be a bit resentful of the wealthier citizens of the community--especially the proto-professionals at Carnegie Mellon University. It seems obvious that a person's salary should be proportionate to that person's power.