FileInsight by Secure Computing (now McAfee)
This is a pretty slick little application that allows for basic file disassembly. Kind of like an OllyDbg-lite.
FileInsight Download (direct link)
McAfee has a nice quick tutorial on this tool (from Avert labs), which outlines the features of this tool well. I’d also recommend taking a look at the following PDF which demonstrates using this tool to uncover an exploit: