This is the thing bugging me. I'd like to see some of my files in binary or plaintext format, but I can't figure out how to do it for all files. I can open some image files in plaintext using Textedit, but that's all I can figure out. Anyone know anything?
I'd recommend BBEdit (used to be TextWrangler) as a good general purpose plain-text editor. If you have this in the Dock, you can drag any file on to it and the file will be opened as plain text.
I use HexEdit for this sort of thing. It can open any file and give you its hex and plaintext representation.
The editor of my choice for these kinds of things is Smultron.