Add this to the QWERTY/Dvorak files:

The TypeMatrix ergonomic keyboard offers a layout with the caps, backspace, and enter keys running down the middle. And it supports both QWERTY and Dvorak layouts with the help of translucent skins that lay over the keyboard. Typematrix also has a Dvorak typing tutorial that can be downloaded from its web site.

Here's a review to check out, and another from a few years ago on SmartComputing.com.

One more option if you're in search of one.