I've just added a new state page for Hawaii, with three Polk directories from the days when Hawaii was still a kingdom! These come from Ulukau, the Hawaiian Electronic Library and are free to view. I know that Ancestry has city directories for Honolulu as well and these will be added in the future. Also, the Hawaii GenWeb site has transcribed online historical medical directories. So stay tuned for these in the future.
Hawaii online historical directories are very difficult to find, so if you know of any other than the above resources, please e-mail me.