Khexedit is probably the easiest and most capable binary file viewer, but there is ghex (gtk based) and hexcurse (ncurses based) and several others as well. A google search for "linux hex editor" is a good start.
If you are just interested in the readable content of the file you can use the command
Code:
strings /path/to/file
to view the content in a console. (man strings for options)