How can I display editable content on my blog sidebar?

The easiest way I found to do this, without adding plugins, etc. is to do the following:

1.  Add a new page, called something like "Sidebar Content".  Add the content you want to display, using images, links, etc (keep in mind the width of the sidebar especially with image widths.

2.  On the main "Edit pages" page, mouseover the page name (Sidebar Content), and note the URL at the bottom (page_id / post_id=) Get the post id number and write it down.

3. Edit your theme page - sidebar.php , or the correct area where your sidebar content should display.

4.  Add this chunk of code where you want the sidebar content to appear (replace "39" with your actual page id obtained in step 2):

<?php
$recent = new WP_Query("page_id=39");
while($recent->have_posts()) :
       $recent->the_post();
        the_content(); 
 endwhile;
?>

Now you can edit the page anytime, to edit the sidebar content!