The best cert that you can get for the least amount of time in school/training IMHO is Power Engineering. Beside the previous cert, elevator mechanic, instrumentation control, and refrigeration are some of the best certs that you can get.
My plumbing/gas fitting certs enable me to have less stress, shorter work week, and higher pay than my old IT job that I got with BS compSc, MCSE, CNA, and A+.
And, currently I'm on my way to finish up refrigeration cert.
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According to my brother that is an IBM employee, Cognos is one of the best cert to have if you are a developer.
Median Salary by Job - Skill: Cognos (United States)