Dissy is a small utility which can be used to disassemble executable programs. It is actually a front end to objdump. On ubuntu objdump is provided by the binutils package.
You can install dissy with
sudo apt-get install dissy.
For trying out dissy, write a small C program as below.
$ gcc -o hello hello.c
Now invoke dissy as
$ dissy hello
You will get a graphical screen as below.