The only e-ink device I know which is not already in your collection is the Hanvon N800, available only in China. I found it on Aliexpress for an outrageous price:
http://m.aliexpress.com/item/32459149040.html
It does have some nice features like handwriting support, sound recording, great battery life, and a solid build, but it's not worth that price unless you are a hard-core collector.
I bought mine for less some years ago, but I'm not ready to part with it just yet 😃
I won't go into color tablets because there are too many to list...