The IT Support Handbook by 
A+ Guide to IT Technical Support (Hardware and Software) by 
A+ Guide to Hardware by "Online Tech Dictionary for Students, Educators and IT Professionals"
IT Fundamentals is a free online course that covers computer hardware, computer software, networking, security, and other basic IT topics.
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Association for Computing Machinery (ACM)
Association of Information Technology Professionals (AITP)
Association for Women in Computing (AWC)
Network Professional Association (NPA)
Computing Technology Industry Association (CompTIA)
Information Systems Security Association (ISSA)
International Association of IT Asset Managers (IAITAM)
Society for Information Management (SIM)
American Society for Information Science and Technology (ASIS&T)
Information Technology Association of America (ITAA)
Computing Research Association (CRA)
International Association of Computer Science and Information Technology (IACSIT)