Low level clouds Names like Workday and ServiceNow may not attract the most attention, but they resemble some of the cloud firms that may look to go public in one important respect: They can lay out lucid metrics, including attractive profitability road maps, to potential investors.  Most won't ever be hot household names—they target enterprises, not consumers—but the public market is increasingly aware of the investment allure of the cloud: software as a service (SaaS), in which cloud providers help lower clients' IT costs by hosting their software and data.  As more businesses continue to move their IT services, applications and infrastructure to cloud-based solutions, global spending is expected to surge.  "How they're going to make money is clear," said Sanwal at CB Insights. "Before they go public, [these firms] have been generating revenue and there is less of that uncertainty that leads to more of the swings on the consumer side of things. They're a little less volatile."  (Read more: Spotify job posting leads to IPO speculation)  According to Bryan McLaughlin, a deals partner at PwC, cloud companies in the SaaS category (think younger versions of Salesforce.com, the granddaddy of cloud applications firms) could be among the year's most solid investments because they possess two distinct characteristics.  "The IPO market yearns for two things in a profile of a successful candidate: growth, which drives valuation of the business, and predictability, which mitigates downsize risk for the investor," he said.  Most SaaS companies charge either a licensing or a subscription fee to use their service for a certain amount of time, benchmarks that make revenue growth readily apparent for investors.  "It's not about upselling your existing customer base—it's about how do you expand that base," McLaughlin said.  A number of SaaS companies are in Renaissance Capital's IPO pipeline, including Amber Road (global trade management), Q2 Holdings (banking services), Paylocity (payroll) and Globoforce (human capital management).  But the Renaissance's shadow backlog contains storage firms Dropbox and Box. The latter recently closed a $100 million round of venture capital funding and reportedly filed its IPO paperwork earlier this year. (Dropbox, with 200 million users, reportedly holds a valuation of $10 billion.)  Analysts point to another segment in the cloud with the potential to turn out lucrative IPOs: Middleware, or companies (such as MuleSoft and WS02) that provide services that combine entities' disparate programs.  "It's about flexibility," said Summer, noting that cloud-based middleware hasn't seen the investment that SaaS and storage have.  "When you have a complicated IT infrastructure with not just one application but 50, some of which may be custom built and they all have to talk with each other—how do you optimize that?" he said.  One thing is for sure: If the pace of companies filing IPO paperwork keeps up, the U.S. IPO market is set to soar this year.  According to Renaissance Capital, 35 firms have already priced in 2014, up 75 percent year over year—the best annual start since the mid 2000s.  Software, which encompasses cloud firms, is expected to do well even at the pre-IPO venture capital stage.  "The software category, with the exceptions of a few bumps, has led the way in terms of funding," said McLaughlin at PwC. "And we're definitely looking for this same trend in 2014."  In a more fundamental way, the cloud will propel the IPO market in coming years, even when its own companies aren't the ones conducting offerings. Cloud computing has affected how startups across many sectors operate: New companies can rent infrastructure from companies like Amazon rather than having to build from scratch. Venky Ganesan, a managing director at Menlo Ventures in Menlo Park, California, said, "We're seeing companies growing faster than at any time in history." That means startups can be ready sooner to go public or be acquired.  —By Maggie Overfelt, Special to CNBC.com, additional reporting by Joel Dreyfuss
Mass storage companies get lots of attention in the cloud IPO buzz but may rank second in their own sector.