Significant speedup:

APC <- alternative php cache

view cache (under view’s configuration:

View content cache:  http://drupal.org/project/views_content_cache

css/js aggregation: https://drupal.org/project/advagg

Other modules:  Boost, authcache

Configuration -> Development -> performance:  enable whatever cache checkbox you see.

Disable developer module putting ?blah after css and javascript files, since this prevents caching.