Facebook isn’t the only blockbuster IPO on the block by Michal Lev-Ram @FortuneMagazine January 31, 2012, 2:15 PM EDT E-mail Tweet Facebook Google Plus Linkedin Share icons FORTUNE — While everyone in Silicon Valley is talking about Facebook’s imminent IPO, a handful of fast-growing yet far-less-sexy enterprise technology companies are quietly eyeing the public markets. True, their valuations are nowhere near the $100 billion Facebook is expected to drum up. But here’s why you should care: Enterprise software is a huge business undergoing serious transition. Giants like SAP SAP , Oracle ORCL and Cisco CSCO are trying to reinvent themselves, and in the meantime smaller players are gaining market share with new approaches to developing and distributing software. The move from on-premise to cloud-based software in particular is spawning promising IPO contenders. Here are a few of the enterprise companies expected to file for IPO in 2012: ServiceNow: When Facebook’s IT workers aren’t day-dreaming about cashing in and buying a mansion in Los Altos Hills, they’re using ServiceNow’s cloud-based IT management software to track problems, manage costs and even develop apps. San Diego-based ServiceNow has scored plenty of big customers — not just Facebook but also rival Google GOOG , Publicis Groupe and REI, to name a few. Last April the company brought in a new CEO, industry veteran Frank Slootman (his previous stint was running Data Domain, which sold to EMC EMC for $2.4 billion in 2009). Last year’s revenue came in at $135 million, and Slootman has been on a hiring rampage. Of course, a focus on IT management won’t make ServiceNow the next Oracle. But the company is betting its platform-as-a-service offering, which IT workers use to build and deliver cloud-based apps, will help broaden its business. Workday: Believe it or not, human capital management tools (industry-speak for the kind of software HR professionals use to manage employee benefits, set staffing budgets and track new hires) is a hotly-contested market. Last month SAP announced it was buying San Mateo, Calif.-based SuccessFactors for $3.4 billion. It’s rumored Workday’s co-CEOs (Dave Duffield and Aneel Bhusri of PeopleSoft fame) passed up multiple buyout bids, and there’s been speculation that an IPO will take place in the second half of this year. The company reportedly doubled its bookings last year, up from $150 million in 2010. And here’s the best indication that an IPO is imminent: Earlier this week a Workday spokesperson told FORTUNE the company is “no longer commenting on anything related to a potential IPO.” Palo Alto Networks: Despite the lame name (it’s offices are in Santa Clara, not Palo Alto), this smallish security company has plenty going for it. Research firm Gartner recently called it a leader for its “disruptive influence in the firewall market,” and its next-generation firewall technology is giving Cisco and Juniper Networks JNPR a run for their money. Last August Palo Alto Networks announced its orders were above the $200 million mark, and the company has said it is already profitable. A few months ago it also brought in new chief executive Mark McLaughlin, the former CEO of VeriSign, to help “take the company to the next level.” And we all know what that means.