If you use the standard wp_list_pages tag it will show every Page you make - unless you exclude them manually (every time you create a new Page). It's a pain... I know.
In many cases if I need a horizontal navmenu for several Pages (like About, Contact, Search, Whatever) I just create a separate file with that hardcoded list and include it wherever I need it. In this way I can use the template tag (and I have to exclude only once the Pages that are in the navmenu) and the template tag can display all my other Pages in the sidebar.
It's just one possible approach.
Another thing - if you are into coding, since WP 2.0 you can hhave a functions.php file in every theme folder where you can define your own functions for that theme.