I would suggest using a program installed on the computer to do the posting. Email posting is a good option, but using a program will let you post to several blogs from one interface, attach posts to categories that are on the blog you are posting on at the moment, etc.
I am using BlogDesk, shareware for the Windows pc. It supports Wordpress, Movable Type, Drupal, Serendipity, and several more (no blogger though). I know there is one that is even better for the Mac, but cannot recall it just now.
Check it out.