That’s DRM free legal ones, that is.
Answering this question for a friend on Twitter, I thought I’d posted my links here, but evidently not, so;
Safari (also OReilly, but subscription with ‘tokens’ for chapter downloads – not signed up for this yet, but really should based on how much I’ve spent on their ‘deal of the day’)
Safari (via the Cambridge Library, if you have a library card)
Fictionwise – the first people to do commercial DRM free eBooks of living authors, from way back when. Most new content contains DRM these days, but they have a lot of out-of-print and short story stuff at reasonable prices – I’m still reading my way through the stuff I bought there..
Webscription – a number of publishers use this as their portal, and it seems to do most formats (crucially, epub, mobi and PDF)
Some others that might be of use, but I’ve not used, and you can’t get the latest ‘blockbuster’ from..
Feedbooks; not read anything from them, but linked via Aldiko.
Genre Specific – go by recommendation only; drivethrurpg.com RPG related works inc fiction (checkout Eclipse Phase and Shadowrun for examples)
Mixed – both Fiction & Reference
Archive.org/openlibrary.org (the latter has some interesting proposals for DRM-aided lending eBooks that I haven’t fully explored yet -and may not as its Win/Mac only due to the dreadful Adobe Digital Editions)
Project Gutenberg – the original eBook project digitising out of print texts. I recently bittorrentted (as they encourage, and I left the torrent open for a couple of weeks to give something back) the DVD they make available of all their books – 7.8GB of text!
eBook friendly publishers
Tor – they often do free downloads of authors works inc commissioning short stories (and when launched gave away loads of eBooks); worth keeping an eye on.
Night Shade Books (via webscription, above)
eBook friendly Authors
Cory Doctorow – one of the first; you can often find eBook apps like Stanza and Alkido with sections to download his works, as they;re all Creative Commons licensed. He also writes some though provoking commentary on the eBook market, including some columns in Publishers weekly that are worth seeking out (but also see below)
Charles Stross – well worth reading his blog for his thoughts on the industry and technology.
The Dragon Page – Cover to cover; slightly cheesy but usually has interesting information each week, and at least one of the hosts makes money from fiction eBooks.
Calibre – eBook management; works on all three OS’s, handles all file formats
Aldiko – Android eBook reader with built in download sites & options fro free/creative commons books
Stanza – iPhone (Ios I suppose I should say) client similar to the above; now ceased development because (IIRC) they were bought by Amazon and it became the Kindle App.