Here’s how to include different sidebars for particular pages:

<?php
if(is_page()) {
 // We're on a "page", which?
 if (is_page('About')) {
 // Ah, the about page!
 get_sidebar('about'); // includes sidebar-about.php
 } elseif (is_page('archives')) {
 get_sidebar('archives'); // includes sidebar-archives.php
 } elseif (is_page('contact')) {
 get_sidebar('contact'); // includes sidebar-contact.php
 } else {
 // if we're not any of the above pages
 get_sidebar(); // includes regular sidebar.php
} else {
 get_sidebar(); // includes regular sidebar.php
}
?>

If you want to extend it further, such as displaying different sidebars for different categories, use this code:

< ?php
if(is_page()) {
    // We're on a "page", which?
     if (is_page('About')) {
        // Ah, the about page!
          get_sidebar('about'); // includes sidebar-about.php
    } elseif (is_page('archives')) {
          get_sidebar('archives'); // includes sidebar-archives.php
    } elseif (is_page('contact')) {
          get_sidebar('contact'); // includes sidebar-contact.php
    } else {
        // if we're not any of the above pages
          get_sidebar(); // includes regular sidebar.php
} else {
    get_sidebar(); // includes regular sidebar.php
}
?>