<?php      if(is_user_logged_in()) {         wp_list_pages('sort_column=menu_order&depth=2&title_li=&exclude=104,101');     }      else {         wp_list_pages('sort_column=menu_order&depth=2&title_li');     } ?> 

If you're using version 2.7 or later, what about this?.
Displaying code snippets from WordPress custom fields

<? if (is_user_logged_in()): ?> <a href="<?=wp_logout_url()?>">Log Out</a> <? endif; ?> 

or (if you want both log in and log out links):.
Converting a static site to a Wordpress site…how to transfer/convert SEO rankings?

<? if (is_user_logged_in()): ?> <a href="<?=wp_logout_url()?>">Log Out</a> <? else: ?> <a href="<?=wp_login_url()?>">Log In</a> <? endif; ?> 

Note that you can give wp_logout_url() and wp_login_url() a single string argument containing a URL to which WordPress will redirect the visitor after login/logout..
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Another Option

If you want the default WordPress login/out link without the ability to customize the HTML and are using at least version 1.5, try wp_loginout():.
Wordpress: Customising output of wp_nav_menu, adding a div before nested ul

<p><?=wp_loginout()?></p> 

(Again, you can optionally provide a string URL redirect-to argument.).
Mediawiki & Wordpress integration - but user database from *mediawiki*
Hope this helps,

How to achieve Post-Redirect-Get in a Wordpress plugin's admin menu page?
Ben.