WordPress Plugin: WP-keitai-mail

It’s not technically a plugin, nor a hack, rather a standalone script that interfaces with WP to let you post entries to your blog via Email.

A quick roundabouts of the current features:

Works as a script executed on email reception (unlike WPâ€™s built-in feature), which means you do not have to run a cron job and your posts appear instantaneously on your blog.
Handles jpeg pictures, will automatically create a thumbnail if they are too big and insert all necessary code in your post.
Can be run on a separate machine from your WP install: it uses xmlrpc to post the entry and can be set to use ftp to upload the picture files.
Can handle as many blogs and authors as you want. For each email account you can customize any aspect of the posts (image formatting, posting category etc). For example, you can easily set up the script to let 5 authors post to your blog with each one under a different category.