That's a very interesting question ^^ I have read some using the default viewer and zooming, but it was too comfortable...
I might try to eventually code one someday (not now though, exams :s), and am trying to find new and innovating ideas...
Possible solutions (or a mix of all of them) :
1. Easiest : landscape mode, scale page (with a nice filter) to 320px wide, and use the finger or pad to scroll up/down... Could work fairly decently, though might be hard to read certain small pages
2. Eye-candy power : landscape mode, zoom out 2 pages side by side (as it fits). The different images shouldn't be any smaller than like 48x48, so that's clickable using a singler finder... Which means that if we can auto-detect all the seperate images in the page, we could do a really cool zoom in effect to maximize the image size... Clicking once to zoom the image, once again to set the image back in the page preview... Would make the text perfectly readable on small images, wouldn't give much benefit on page-wide images though... Would be a problem for big images (=> revert to solution 1 in that case, I guess)
3. Portrait mode, show a whole page, and zoom on the part you touch with a loop effect... would give the best quality page preview, not sure how simple it would be for text reading though :/
4. Buy an ebook
Any other ideas ?
edit : the other idea was to detect text/text bubbles, but by looking at some mangas I saw there were quite a few texts written directly onto the image which we can't detect :/