A recent contributor to the brilliant GigaOm is Baris Karadogan (a partner at Comventures). His point is an update of an old IBM notion about how few mainframe computers we needed 50 years ago - his current version is that five computer “clouds” could allow us to do everything we want (Clay Shirky of NYU has said this is off by four... point is that we all just need one cloud). Baris' picks are Google; Amazon; Salesforce.com; either Sun Microsystems or VMWare; and Akamai.
1 - Google Products provide all the (mostly ad supported) apps and communication tools we use for email, social networking, sharing and blogging. Of course the "MyFaceTube" Social Network services are coming and going (to be bought).
2 - Amazon Web Services give online-based solutions for developing and hosting consumer web apps. Scalable, on-demand, cheap-pay-as-you-go.
3 - Salesforce.com is the CRM engine for business. It should start integrating into your financials to be a single solution.
4 - Sun Microsystems is the reigning enabler of enterprise infrastructure - servers, storage, etc. This is a big "etc" as Sun continues to evolve and reinvent. I highly suggest Jonathan Schwartz's eloquent Blog to get a handle on the present and future of computing from Open Source initiatives to this post on the parallels between cooking and ecotrends (hugging customers, not trees).
Watch out because VMWare is disrupting this space
5 - Akamai is the top Content Delivery Network that gets all the bits to where they need to be.
Consider where your business intersects the 5 clouds. Your success depends on how you take advantage of these resources... and/or compete with them.
For healthy conversation and contradictions to this, go here to see the reader feedback from the GigaOM post.