No. Websites that offer bare product keys for about 85% off of full price are scams. Those sites are selling illegally obtained MSDN product keys and not retail keys. Such keys get blocked by Microsoft in a few weeks.
Microsoft requires that retail product keys are only sold with Windows software.
If you scan some of the threads in this forum you will see how many people are being taken by crooks selling counterfeit Windows on eBay (more than half on eBay are fakes), Amazon Marketplace, and discount websites.
Take a look at this
http://www.youtube.com/watch?v=hzqNNiOM0cs
Colin Barnhorst Windows 7 Ultimate x64 on DIY with 6GB ram.