Iriver Story comic viewer
Well, I have only used it occasionaly, my impression is generally positive.
It can handle CBZ archives (if you have CBRs you have to convert to CBZ, easy to do en masse via command line).
Page turning speed is good but depends on the picture size, and contrast is acceptable: this is a 8-level grayscale 800x600 screen, so if you want to get optimal results you have to pre-process.
Worth noting: the Story managed to display sequentially a comic which was scanned with two pages on one picture, i.e. it displays the left half of the picture, then the right half, then next pic.
With current firmware (1.10) it is not possible to rotate pics for landscape viewing.