Valuable websites and tutorials
CBT Tape - Hundreds of freeware MVS Utilities ready to install.
IBM Mainframe Forum - the biggest MVS forum out there.
Mark's MVS Utilities - more scripts.
Tutorials Point - basic JCL course. Good for beginners.
IBM Academic Initiative - great videos describing basics of z/OS.
Kumar IT - tons of valuable video tutorials related to many z/OS areas.
Rui Miguel Feio website with a lot of interesting articles.
Mainframes.com - one more website with tips & tricks.
LBD Software - free z/OS tools.
CSIS COBOL programming course.
Mainframes Tech Help - Great tutorials. Also, on quite rare subjects like IMS and CICS.
Mainframe Tips And Tricks - A lot of interesting articles and tips on various z/OS topics.