Tor books does not have it's own store and they sell via amazon etc so we usually wouldn't list them separately but they are big publishers and many have requested we add books by them so I have added their ebooks from amazon and listed them as amazon Tor Books. See
http://drmfree.calibre-ebook.com/by/...n-tor?by=title
Tor Books on amazon.com are DRM-free. For some reason they do not have an entry saying "Simultaneous Device Usage: Unlimited" under product deatils which is usually the indicator of a DRM-free ebook an amazon. Instead they have a statement in Book description saying "At the publisher's request, this title is being sold without Digital Rights Management software (DRM) applied."
To find Tor books on amazon click on
http://www.amazon.com/gp/search/ref=...oks-Submit.y=0
above link was obtained by clicking on Advanced Search under books, selecting the Kindle format and entering the publisher.
The information on how to find Tor books on amazon.com was posted by Bufo Calvin on
http://www.amazon.com/forum/kindle/r...TxQ3BMS6ZZOVY8