If you still want an answer to this question, there are no other hidden service email providers. TorMail provides a great service for the community. However, you can create email accounts over Tor on some clearnet webmail providers. I know that Yahoo Mail, Safe Mail, and Yandex work over Tor. Safe Mail is the best option, because it uses SSL by default and has a simple interface which you can use with JavaScript disabled. You'll want to turn off IP checking, otherwise it will log you out when you switch exit nodes after 10 minutes.