Microsoft has started accepting pre-orders for multiple versions of Windows 8. Boxed retail products, OEM copies and even product key cards are starting to appear online at various retailers in the US including Amazon, Best Buy, the Microsoft Store, Office Depot and Staples.

Pricing starts at $69.99 for Microsoft's Windows 8 professional upgrade and the pro pack product key card. Users can elect to pick up the full OEM version of Windows 8 in 32- or 64-bit flavors for $99.99. Those after the professional edition can expect to pay $139.99.

If a boxed retail version isn't for you, Microsoft suggests waiting until October 26 to upgrade online. Using the Windows 8 Upgrade Assistant, consumers will pay just $39.99 for the update. Online upgrading to Windows 8 Pro will be supported in 140 countries, 37 languages and 23 currencies worldwide.

Finally, Microsoft reminds us that consumers who purchased (or will purchase) an eligible Windows 7 computer between June 2, 2012 and January 31, 2013 will be able to take advantage of discounted upgrade pricing. Expect to pay just $14.99 for an upgrade to Windows 8 Pro starting October 26. Details on how to redeem this offer can be found here.

Microsoft spokesperson Brandon LeBlanc was quick to highlight the packaging used for retail DVDs in a blog post earlier today. The rep said boxes consist of one of five vibrant illustrations and is constructed completely from paper, a move that allowed Microsoft to reduce greenhouse gas emissions by 80 percent. The new material also cut packaging weight by 41 percent compared to Windows 7 retail offerings.

LeBlanc also pointed out that consumers will be able to pre-order Windows 8 PCs and devices from OEM partners starting today. Acer, Asus, Dell, HP, Samsung and Sony have all announced new fall lineups featuring Microsoft's new operating system.