Firemail is a new application that does exactly what TouchType does, except that Firemail is free…
As soon as you launch Firemail, it will allow you to type your emails in landscape mode. Type in your subject line and email body, then you can choose to “send to MobileMail”, which opens your default email. From there, you can select the recipient and send the email. You can also “Save to bookmarks”, which saves the snippet of text to use it in another email.
Firemail [iTunes link] is free and is currently your best option for typing emails in landscape mode… well, at least until Apple decides it’s a must-have feature.