IBM is a giant in the enterprise, and no one should overlook it. Valued at $202 billion, IBM’s entire business is focused on helping enterprise companies with their technology needs, and so it brings more resources to bear here than any other company on our list, perhaps with the exception of Microsoft. Amazon and Google, while also large companies, still have most of their resources tied up with the consumer products that made them popular.

IBM knows it has to bet big on the cloud. It needs large companies to continue to rely on it as a technology supplier — and that means furnishing companies with technology that works well with other technologies. Of course, that includes making sure it adapts to the cloud revolution.

Some estimates put IBM’s cloud revenues this year at $2.26 billion. That’s modest, considering the company goal to reach $7 billion in annual cloud revenue by 2015. Notably, IBM expects only $3 billion of that total will come from new business, and $4 billion will be tied to cloud-based ways of delivering its current hardware, software, and services.

Already, IBM is acting as an integrator in most areas of the cloud. Much of its cloud tools are housed under its WebSphere brand. IBM acquired Cast Iron Systems, a leader in helping companies integrate their SaaS applications, in 2010. Websphere competes against a bevy of other younger competitors in the SaaS integration area, including MuleSoft, Snaplogic, Rapier, and Cloudwork.

IBM also owns Tivoli, a technology that helps companies integrate cloud environments.

IBM is also big enough that it could potentially acquire or roll up a bunch of other fast-growing companies in related areas. A host of companies, including Puppet Labs, Opscode, SaltStack, CloudVelocity and others are all helping IT executives administer their infrastructures and workloads in useful ways.

Similarly, when enterprise companies seek to integrate sophisticated data services, IBM Information Management is a leader, along with others players like Greenplum, Teradata, and Oracle.

And finally, in July IBM completed the acquisition of a leading cloud computing infrastructure provider Softlayer. That’s a nice complement to IBM’s existing offering of more than 100 SaaS apps, which cover many fields: marketing, procurement, e-commerce, customer service, human resources and city management.

In other words, IBM has quickly emerged as a big player at every level of the stack.

IBM is so big and slow that it is its own worst enemy. Developers perceive it as serving mostly legacy enterprise customers. But those enterprise customers still have the biggest budgets, and IBM continues to ride with them into the cloud. These are the “guys I lose the most sleep about,” says Leo Spiegel, the SVP of strategy and corporate development at Pivotal, referring to IBM.

If you’ve used IBM’s cloud products, please let us know what you think, and get our free full report when it is released next month.