Cloud computing looks to be a "classic disruptive technology," says Forrester Research in an interesting new report published yesterday. For enterprise IT shops, cloud computing still poses some real risks, including an almost complete lack of service-level agreements and customer references, plus some genuine security and compliance concerns, according to Forrester. But even so, IT shops are tapping into cloud services for targeted projects: "There's a high likelihood that developers inside your company are experimenting with it right now," writes senior analyst James Staten in the report,"Is Cloud Computing Ready for the Enterprise?"

That analysis meshes with what we recently reported hearing from CIOs in "Cloud Computing: Tales From the Front." The cloud isn't new per se; enterprise IT has had access to the Internet and software-as-a-service for years. But now, some vendors are giving enterprises the chance to run not only hosted apps but also custom-developed apps in the cloud—with great flexibility to scale computing power on short notice, and to pay only for what computing power is used. Enterprise IT sees the promise and is experimenting, cautiously.

Which cloud computing vendors should be on your radar screen now? In its report, Forrester cites 11:

1. Akamai
2. Amazon
3. Areti Internet
4. Enki
5. Fortress ITX
6. Joyent
7. Layered Technologies
8. Rackspace
9. Salesforce.com
10. Terremark
11. XCalibre

Akamai, Amazon and Salesforce will be the most familiar to enterprise IT. Akamai offers application performance services that speed up apps for users of cloud services, while Amazon offers the Amazon Elastic Compute Service (EC2) and storage in the cloud. Salesforce is pushing hosted apps and what it calls Platform as a Service, to help developers create new software in the cloud.

Terremark, Layered Technologies, XCalibre and startup Enki all play more behind the scenes in the hosting business that fuels and manages the cloud.

Also prominent at the moment is 3Tera, maker of AppLogic, which Forrester describes as "cloud computing infrastructure software" and a "grid engine." Basically, this is enabling software that lets a hosting provider put customer software in the cloud with a minimum of fuss, for starters. AppLogic works on physical servers and virtualized ones, enables cost-based reporting, and runs many applications "without redesign or reprogramming to a grid API," among other benefits, Forrester notes. Check out the report for more details on all the vendors and Forrester's take on the competitive landscape.

No doubt, cloud computing, especially as Amazon envisions it, is in its early days, complete with hype and confusing jargon.

Nonetheless, for IT execs, the sooner that you tune into how people in your enterprise are playing with the cloud, the better, Forrester's Staten says. "Even if IT can't justify leveraging clouds, your business units will," he notes in the report's conclusion. "Cloud is a compelling business proposition, infrastructure they can provision with a credit card, with low barriers to entry and to exit. Rather than block their efforts, learn from them."