Amazon Kindle Cloud Reader
I think Amazon had this in the works for a long time — a web-based Kindle reader has been around for a while, and it makes sense to improve it in these ways. But surely Apple’s new App Store rules for paid content have motivated Amazon to push harder in this direction.
It’s a good start, although it doesn’t support collections or periodicals yet. With Kindle now fully protected against future App Store changes, there’s even less reason to by content from iBooks.
Update (2011-08-11): A JavaScript bookmarklet to make the text selectable in Safari.