Magento 2 - Uninstallable set of packages when deploying magento-sample-data

Had the same problem. Fixed with going to the root directory and specifying the repositories for composer with the following command (use https to avoid composer warning):

composer config repositories.magento composer https://repo.magento.com

After that

cd bin
php magento sampledata:deploy

worked as intended

I've also been struggling to install the sample data. It appears that somthing is currently broken here (Oct 2015) and the instructions in the devdocs didn't work for me either. I was experiencing the same composer issues and the magento sampledata:install isn't even there.

Instead I've been following the "From GitHub Repository" instructions on the sample data's readme file:

Just clone the repo somewhere (can be outside your project folder, since the tool is taking care of symlinking the individual modules):

git clone https://github.com/magento/magento2-sample-data.git ~/sample-data

Then run the "installer" script:

php -f ~/sample-data/dev/tools/build-sample-data.php -- --ce-source="$PATH_TO_YOUR_MAGENTO2_PROJECTROOT"

After that run the update script:

cd $PATH_TO_YOUR_MAGENTO2_PROJECTROOT
bin/magento setup:upgrade

And you should see the sample data being installed (takes a while...):

[...]
Module 'Magento_DownloadableSampleData':
Installing data..
Module 'Magento_ThemeSampleData':
Installing data..
Module 'Magento_OfflineShippingSampleData':
Installing data..
Module 'Magento_ConfigurableSampleData':
Installing data..
Module 'Magento_BundleSampleData':
Installing data..
Module 'Magento_ProductLinksSampleData':
Installing data..
Module 'Magento_ReviewSampleData':
Installing data..
[...]

Don't forget to clear caches and fix permissions and you should see all the sample data in the backend and the frontend now...

In the first section, add "minimum-stability": "beta", before license.