Drupal's CSS optimization, once turned on, will roll all of these up for you automatically, so if you aren't using Drupal you will need some sort of build system to combine and minimize everything. But I think this is a good start.
On a side note, I really like the method the Zen theme uses for CSS columns. Worth checking that out as well.
html-reset.css layout-fixed.css page-backgrounds.css messages.css pages.css blocks.css navigation.css comments.css forms.css fields.css print.css ie.css ie6.css
Drupal's CSS optimization, once turned on, will roll all of these up for you automatically, so if you aren't using Drupal you will need some sort of build system to combine and minimize everything. But I think this is a good start.
On a side note, I really like the method the Zen theme uses for CSS columns. Worth checking that out as well.