Executing programs securely

How do I exec thee?  Let me count the ways:
Good choices:

    execl( const char *path, const char *arg, ...);
    execle( const char *path, const char *arg , ..., char * const envp[]);
    execv( const char *path, char *const argv[]);

Bad choices:

    /* doesn't have path hard coded - depends on $PATH variable */
    execlp( const char *file, const char *arg, ...);
    execvp( const char *file, char *const argv[]);

    /* sends command to shell via "sh -c " -- if user input is included  */
    /* in the command, they may sneak shell metacharacters in */
    /* use pipe / fork / exec instead */
    system( const char *string);   
    popen(  const char *command, const char *type);