Try this sample. It is available for all matter of reading devices. No harmful side-effects are reported as of yet.

Adobe PDF for computers of all shapes and sizes. If you have a portable reading device please do not download this one.

For PCs. Most ebook reading devices can handle them but there are better, more optimized formats for those (see below).

Epub for Apple devices, Sony Readers, Kobo readers, any kind of ebook reader that isn't a Kindle.

For Apple devices, Nooks, Sony Readers, Kobo Readers, just about any kind of portable reader that is not made by Amazon. Current industry standard and the most feature-rich ebook format.

Mobi (Proprietory: AZW3) for Kindles and the Kindle app.

For Amazon Kindles and the Amazon Kindle app on smartphones and tablets. Usually those smartphones and tablets also have apps that can read Epubs, though.

Instructions for sending the sample to your device:

For Apple devices (iPhone, iPad, iPod touch): import the .epub file into the iTunes library (File>Add to Library) and sync to your device (File>Devices>Sync [name of device]).

For non-Apple devices: Add the .epub file to your library in Calibre using the "Add Books" button and click the "Send to Device" button to get it on your reader. You can also use the software provided by the manufacturer of your device. You're on your own there, friend.

Kindle: Follow the steps above using Calibre or add the .AZW3 file to the Documents folder on your Kindle device. Unfortunately Kindle for PC does not sync .AZW3 files unless they are purchases from Amazon.