[colinmb]

I'll add another recommendation for the freeware version of IDA 5, a copy of which the ScummVM project has permission to host. Although it's Windows-only and its UI feels a bit clunky today, the keyboard shortcuts allow an experienced user to be pretty efficient in navigating code, assigning data types, changing symbol names, etc.

I was especially pleased with IDA 5's ability to find and organize all the segments in just about any MZ EXE I've used it to reverse. It was even able to deal with the overlay segments in a Borland VROOMM / FBOV executable, and that was a pretty short-lived endeavor that faded to obscurity as soon as DOS/4G was on the scene.