Unlike other eBook stores, Amazon does not offer .epub's (a free and open eBook standard) for their Kindle devices. What they do offer is a proprietary format that only will work on their own Kindle devices. Sadly this creates user lock in as there is no way to take those digital titles to another reader without stripping the DRM from them (something that may or may not be illegal in certain countries) and converting to a format that does work on said other devices.
Amazon being as large as they are can often undercut the pricing of eBooks. This is not always the case as a lot of eBooks have their prices set by the publisher. this is called agency pricing. But on non-agency eBooks Amazon is often the cheapest store.
Amazon offers the Kindle app for just about every platform. So far there are apps for Android, iOS, Blackberry, PC, Mac, and Windows Phone 7. Conspicuously the Linux platform is absent from that list.
Amazon offers an unlimited (actually it is pretty limited) eBook service similar to what netflix offer for movies. Though the selection is on the smaller side compared to their regular eBook store.
Large selection, but there is an ever increasing numbers of books that are less than 100 pages, mainly created copying and pasting freely available information from the web. Searching for what you want is becoming difficult, with results showing lots of pointless and poorly written small books.
The Amazon Kindle store allows for users to send eBooks as a gift to any e-mail address of their choosing along with a custom message, though for now this feature is US only.
The Kindle Owners' Lending Library is a feature of Amazon Prime, a service that costs $99 a year that includes such features as free two day shipping on Amazon orders and a membership to their video and music services. The Kindle Owners' Lending Library has more than 600,000 books users can borrow (one at a time) with no time limitation.
Amazon offers discounted eBooks daily for their "Kindle Daily Deals". The eBooks can be as much as 80% off the normal retail price. Though often the eBooks on offer of of low quality or unheard of titles.
For some reason not all the eBooks available on the Kobo eBook site are downloadable as .ascm files. Most likely Kobo leaves this up to the publisher, as Houghton Mifflin Harcourt does not have a single book on the Kobo store that offers a separate .ascm download. What most users are unaware of is that the Kobo store is not primarily an .epub bookstore. Kobo uses a proprietary format called .kepub that only works on their own Kobo branded devices. Many of the books they sell do offer a separate .ascm file download, but not all. What exacerbates this issue is that there is currently no way for a user to know if an .ascm will be offered until after purchase.
The Kobo eBook store offers a separate file download (most of the time) from within a users browser. this file is called and .ascm file and is what is used to add an .epub to the Adobe Digital Edition software.
Depending on whether a user is logged in, different prices will be shown on non agency eBooks. Non agency eBooks allow for Kobo to set the price of the title instead of the publisher and sadly it does appear as though Kobo has taken advantage of this to entice new users into thinking their books are priced lower than they actually are.
Kobo often offers a lot of coupons for their eBook store. Some being as high as 80% off coupons. Though most only work on non agency eBooks, so not that great if the user only reads the newest of releases.
eBooks.com offers free excerpts for their more popular eBooks. This way users can get a feel on how the title reads and what it's structure looks like.
eBooks.com allows for users to purchase gift certificates online worth 10-100 dollars and will then e-mail said certificate to an e-mail address of the purchases choosing along with a customized message.
All eBooks for sale on Books on Google Play are Adobe Digital editions compatible. Google provides an option to download an .acsm file for all eBook purchased on their site. This .acsm file can then be imported into Adobe Digital editions where it can be read as an .epub inside of the application or transferred to any Adobe Digital Editions compliant .epub eReader, such as a Kobo.
Goolge has built in a function to allow users to upload their own eBooks. Up to 1,000 files can be stored using this function as long as each title is below 50MB.
Upon close inspection Books on Google Play does not actually follow the normal standards when displaying user uploaded .epubs but rather has it's own secret method of how it handles the internal .css and HTML. This can result in display problems for user uploaded content.
iBooks does use .epubs for its eBooks but sadly they are encrypted with their own proprietary DRM called Fair Play. This means any .epub that has Apples DRM purchased from iBooks will not be able to be used in other .epub eBook readers.
There is no webpage for the iBooks Store which means there is no way to browse Apples eBook selection without using one of their device or installing iTunes.
Harlequin use to offer self publishing under the name Harlequin Horizons but under criticism was spun off and renamed DellArte Press. So users can self publish with DellArte Press but it will not be under the moniker of Harlequin.
Harlequin does still offer a way for anyone to submit their book to them but it is no guarantee it will be published.
Instead of developing their own eBook store, eReaders or reading apps WHSmith has the instant gratification of offering quality products with an established brand.
A good thing about the WHSmith eBook store and its Kobo partnership is that it creates competition in the UK for eBook stores and devices. WIth competition comes better prices and innovation.
WHSmith has entered a contract to where they are now partnered with Kobo. With this deal WHSmith has replaced their old eBook store with a Kobo powered alternative. Basically it is just a WHSmith skin over the Kobo eBook store.
While B&N does use and read .epub on their devices, any eBook purchased from the B&N eBook store will not be able to be used in other .epub readers unless the DRM is stripped from said eBook.
B&N offers a NOOK app for Android, iOS and Windows 8 in their respective stores. This allows user to shop and read their eBooks natively on those operating systems.
Part of the reason B&N is having so much trouble with the NOOK brand currently and most likely part of its decision to separate itself from it by spinning it into its own company is that since the demolishing of agency pricing they are unable to compete on prices.
B&N will be spinning its NOOK division into a separate company, which does not show much faith in their own brand. What's worse is that this show of uncertainty of wanting to separate from the failing device and it's eBook store will only just further distance the customers from the NOOK. Being that their eBooks have a special DRM scheme that does not allow their .epubs to work in other device, current users better hope this new company does not fold or they will be out of their entire NOOK eBook library.
Waterstone's eBook store sells .epubs that are encoded with Adobe Difgital Editions DRM. This allows the .epubs purchased to be used with the Adobe Digital Editions application that can then transfer purchased .epubs to ADE compliant eReaders.
Something of an odd predicament in that Waterstone's has a contract with Amazon to sell Kindle devices even though they only sell .epub eBooks on their Waterstone's branded eBook store.