This was a good list for the intermediate command line user looking to customize. For the absolute newbie I'd reduce it down to git/hg, ssh, grep/ack and curl.
tmux is a CLI terminal multiplexer. As an interactive CLI program, you need a shell to use it. To run such a shell, you need a terminal emulator. iTerm2 is a Mac OS X only GUI terminal emulator.
I don't use any advanced features of iTerm, though, I just use it over Terminal.app because it supports 256 colors. We have not been updated to Lion or Mountain Lion at work so Terminal.app is still limited to 16 colors for me.