Index: wp-includes/category-template.php
===================================================================
--- wp-includes/category-template.php	(revision 15432)
+++ wp-includes/category-template.php	(working copy)
@@ -461,7 +461,7 @@
 		'exclude_tree' => '', 'current_category' => 0,
 		'hierarchical' => true, 'title_li' => __( 'Categories' ),
 		'echo' => 1, 'depth' => 0,
-		'taxonomy' => 'category'
+		'taxonomy' => 'category', 'separator' => '<br />'
 	);
 
 	$r = wp_parse_args( $args, $defaults );
@@ -529,6 +529,7 @@
 		return $output;
 }
 
+
 /**
  * Display tag cloud.
  *
Index: wp-includes/classes.php
===================================================================
--- wp-includes/classes.php	(revision 15432)
+++ wp-includes/classes.php	(working copy)
@@ -1397,7 +1397,9 @@
 				$class .=  ' current-cat-parent';
 			$output .=  ' class="'.$class.'"';
 			$output .= ">$link\n";
-		} else {
+		} elseif ( isset($separator) ) {
+			$output .= "\t$link$separator\n";
+		}else {
 			$output .= "\t$link<br />\n";
 		}
 	}