How do I set a user environment variable? (permanently, not session)

This is irritating me. I seen several suggestions (all using different files and syntax) and none of them worked.
How do I set an environment variable for a specific user? I am on debian squeeze. What is the exact syntax I should put in the file to make ABC = "123"?

ANSWERS:-

You have to put the declaration in the initialization files of your shell:

• If you are using bash, ash, ksh or some other Bourne-style shell, you can add
  

  ABC="123"; export ABC
  

  in your .profile file (${HOME}/.profile). This is the default situation on most unix installations, and in particular on Debian.
  If your login shell is bash, you can use .bash_profile (${HOME}/.bash_profile) or .bash_login instead.
  Note: If either of these files exists and your login shell is bash, .profile is not read when you log in over ssh or on a text console, but it might still be read instead of .bash_profile if you log in from the GUI. Also if there is no .bash_profile then use .bashrc.
• If you've set zsh as your login shell, use ~/.zprofile instead of ~/.profile.
• If you are using tcsh, add
  

  setenv ABC 123
  

  in .login file (${HOME}/.login)
• if you are using another shell look at the shell manual how to define environment variables and which files are executed at the shell startup.