In the publishing world, a book that goes through reprint after reprint is called an "evergreen." In the same vein, there are certain IT certifications that keep popping up in various surveys as desirable.
But are they still worth the effort and investment? In a word, yes. Employers are still seeking job candidates who possess them, and specific certifications open doors to more challenging work and higher pay.
Even so, there's a pretty clear certification hierarchy in many programs, which start at an associate level, advance to professional status and then move from there into master, expert or architect levels.
To clarify the differences, here's a little cheat sheet that breaks down evergreens into entry-level, intermediate and advanced categories.
What makes these credentials evergreen and valuable? The answer varies by category and by perceived demand and cachet.
At the lowest level, the CompTIA "holy trio" (A+ , Network+  and Security+ ) have long constituted a basic set of checkbox items for entry-level IT workers, and are universally taught at technical schools, community colleges, and job training programs.
The Cisco CCNA is the stepping stone to the company's intermediate level/professional (and specialist) credentials . Likewise, the MCSA is an important entry point into Microsoft's popular certifications and acts as a lead-up to higher levels.
At the intermediate level, Cisco and Microsoft continue to attract major mindshare. But this is where other key platforms and technologies — most notably, VMware for virtualization and Oracle for database development and administration — have started to stake out some space. The Project Management Professional credential  teaches IT professionals how to plan, budget, manage and control projects, and has become a go-to "soft skills" certification that can help midcareer pros garner accolades.
Finally, at the advanced level, the Cisco CCIE remains the prototype evergreen IT cert: popular and highly sought after for more than a decade now, despite a difficult, expensive and demanding lab exam. (It costs $1,500 and requires travel to one of only six authorized testing centers.)
The CISSP  is an information security certification without peer. The Oracle and Microsoft master level credentials are scarce, but also document valuable skills for IT workers in specific technical areas including messaging, database, directory services and more. And with the explosion of computing into the virtualized cloud, VMware's pinnacle expert-level credential is in high demand.
Obtaining and keeping credentials current is essential to all IT pros serious about their career. The evergreen certifications outlined here are great places to start.