In Java:  

class HelloWorldApp {
    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}
----------------
In PHP   

<?PHP
echo "Hello World!";
?>  

----------------
In C:

#include <stdio.h>  

main(){
    printf ("Hello World!n");
}  

----------------
In C++:  

#include <iostream.h>  

main(){
    cout << "Hello World! ";
}  

----------------

In Pascal:  

Program Hello (Input, Output);  

Begin
  Writeln ('Hello World!');
End.  

----------------

In Ada:
with Text_Io; use Text_Io;  

procedure hello is
begin
    put ("Hello world!");
end hello;


There is a project out there that is trying to put up examples for different languages.