I been using Scribd a lot recently.
I don't download books, preferring to stick to kindle or iBooks for that, so have no subscription.
But I've found the collections contain lots of useful material which, although it can't be downloaded, can be read online, meaning I can see it on my iPad at home when I'm painting.
Lots of out of print material, inc some of the Montvert series, so a useful resource I'd say.