ebooks/online materials - best format for learners?

I've been struggling to find the most suitable format in which to post longer documents online. Generally I prepare an A4 PDF and then embed via Scribd - as you'll see here: http://strangenewsstories.eslreading.org/travel/flyingchair/flyingchair....

Now I'm trying to get ready for the (supposed) mass switch to ereaders - so I've experimented with the much smaller 7 x 11in format as here: http://ghoststories.eslreading.org/signalman/story.html
This seems to work well enough but not sure if it really suits those using standard computer (the vast majority for some time to come). Also would like to make things print-friendly - but this is an ongoing headache, particularly using non standard page sizes.

How about A5 - which I assume would print two pages to one A4? Any better ideas?

Many thanks

Kieran

http://www.eslreading.org/