The first, to my knowledge, fire and forget Dropbox-based hosted solution. It's a very elegant concept: hook the app up to your Dropbox account, where it watches a folder for new Markdown files. Put one in and it renders it as a new post in your static blog using Pelican.
The only problem is that you have to regenerate the blog every time you want to post. My understanding is that this is due to a limitation in Dropbox's API; it doesn't let 3rd parties automatically monitor for file events.
Calepin supports custom domains. But its longevity is still in some doubt; its creator gave notice that he was abandoning the service, but doesn't exactly seem to have done so. It's still being updated.