Performance modules for all the assets referenced inside the HTML
CDN:
http://drupal.org/project/cdn
http://drupal.org/project/cloudfront
http://drupal.org/project/parallel
http://drupal.org/project/simplecdn
http://drupal.org/project/creeper ?
http://drupal.org/project/sf_cache
CSS:
http://drupal.org/project/css_gzip
http://drupal.org/project/csstidy
http://drupal.org/project/css_emimage
http://drupal.org/project/css_preprocessor
Images:
http://drupal.org/project/xsend
http://drupal.org/project/image_optimize
http://drupal.org/project/imageapi_optimize
http://drupal.org/project/imagecache_smushit
JavaScript:
http://drupal.org/project/javascript_aggregator
http://drupal.org/project/ajaxcache
http://drupal.org/project/closure_compiler