The competitive winds are blowing for Amazon.com today as various rivals ratchet up their efforts against the Seattle online retailer. Wal-Mart, which has been battling Amazon for customers of the now-defunct Circuit City chain, is giving its electronics department a major overhaul in a bid to lure buyers. AT&T is joining Amazon in the cloud-computing business, and document-sharing service Scribd is taking on Amazon's Kindle in the electronic book market.

Wal-Mart is rolling out "roomier and more interactive electronics displays" today, according to the Wall Street Journal, which said the retailer is also adding new high-end televisions, Blu-ray disc players, and mobile phones to its inventory. It's part of an effort to capture market share of Circuit City, which filed for bankruptcy last fall and shuttered its stores this spring. The Journal reports the new Wal-Mart offerings are sparking a "fierce price competition" with Amazon and Best Buy on popular electronics items.

At the same time, AT&T is dipping its toe into the cloud-computing business. It's come out with a computing storage service, along the lines of  Amazon's S3, that gives enterprise customers access to their data remotely via laptops and mobile devices. AT&T is using EMC technology for the new service.

And Scribd, a popular document sharing web service, is testing a new platform to let publishers and others sell digital content including e-books. While none of the major publishing houses have signed on yet, the pricing model provides an interesting counterpoint to Amazon's Kindle store. While Amazon takes up to a 70 percent cut of sales for content on its Kindle reader, Scribd is saying it will give sellers 80 percent of the revenue.

How serious are these threats to Amazon? The Wal-Mart effort to grab more of the electronics market would seem to be the biggest issue at the moment for Amazon, since it goes right to to the heart of Amazon's core ecommerce business.

AT&T is just getting started in the cloud, but any time a company of AT&T's size starts to size up a new market, other players in the space are bound to take notice. As for Scribd, the pricing model certainly grabs attention. The real question there is whether Scribd, which has sparked piracy concerns, can gain traction with publishers who are fed up with Amazon's tight grip on Kindle content.