UPDATE: Angel has now also gone live on the Barnes & Noble Nook Store:
(I believe this may be mainly relevant to readers in the United States. The download price there has been set by B&N at an easy $2.99.)
I've updated the original post to include all of the major sources from which Angel is now available as an eBook, as far as I'm aware. If you know of any others, please do let me know!
Thanks for your interest in Angel and I do hope you'll find reading it worthwhile; the feedback I am receiving is really most encouraging!