You're probably not looking at hardware if you're thinking cloud
I agree it would be interesting to look at cloud deployment options for Hadoop, but that belongs in a separate collection without the word "hardware" attached. Cloud capacity is undoubtedly the hands-down winner where price-for-performance and Hadoop are concerned. Few if any enterprises can buy, provision, and run at Amazon or even Rackspace or IBM SoftLayer economies of scale.
If you're looking at hardware, I'd submit it's not because you think you can achieve a lower TCO than renting virtual racks from AWS. You're choosing to deploy on premises because that's where your organization wants to keep its data (for security, regulatory or other reasons) and it has the people and data-center capacity to explore the opportunity. Maybe you experimented with Hadoop in the cloud, but now you're ready to build an on-premises cluster. This collection is for you.