--- ./app/design/frontend/base/default/template/catalogsearch/result.phtml	2011-02-09 16:24:16.000000000 +0100
+++ ./app/design/frontend/default/default/template/catalogsearch/result.phtml	2011-02-09 16:33:45.000000000 +0100
@@ -53,3 +53,11 @@
     <?php endif; ?>
 </p>
 <?php endif; ?>
+
+<div class="back-button">
+    <button onclick="history.back();" class="button" title="<?php echo $this->__('Back') ?>" type="button">
+        <span>
+            <span><?php echo $this->__('Back') ?></span>
+        </span>
+    </button>
+</div>