Today while working on an AJAX issue for CollegeDistrict.com I came across a need to only see HTML requests to Apache while leaving out all of the many requests for images, css, and js files. This would make it quite easy to see when AJAX requests were making it through properly.
I found the following solution which worked well: http://www.serverwatch.com/tutorials/article.php/10825_3376671_2/Advanced-Logging-Techniques-With-Apache.htm
I used these settings in our development httpd.conf:
SetEnvIf Request_URI "(\.html|\.shtml)$" html CustomLog logs/html.log common env=html