Things for the new student of unix to study, and not to study

Shell choice (the program you type your commands into)

sh, csh and tcsh are around mostly for historical reasons. bash or ksh is a better choice for the new student. tcsh is ok for interactive use, but definitely don't write scripts in csh/tcsh.

Editor choice

vi is very handy once you know it, but new students are better off learning pico, xedit or emacs. Hardcore administrators will want to learn a small number of ed/ex (s, w, q, p, line number) commands (a safer fallback than vi), but this is not a requirement for the average admin, and totally irrelevant for the casual user.

Language choice

The hardcore admin will want to learn some sh/ksh/bash scripting (the three are extremely similar as far as programming goes), and some C or C++. Many people swear by perl, though personally I think it's a particularly poorly designed language, and ranks down there with sendmail in readability. My "main pick" is python: it's appropriate for casual users; professional programmers; quick, throw-away scripts; -and- huge software systems.

Sysad Trouble-shooting tools

A dedicated admin should learn to use snoop or tcpdump (these are sniffers), and truss, strace or trace (these are system-call tracers) - unless your chosen unix variant doesn't have such a thing (bummer!). I prefer snoop to tcpdump. truss is better supported than strace, but strace has an important -s option. trace will do in a pinch, but I'd rather have truss or strace. All of these are tremendously valuable in tracking down problems.

Programming Trouble-shooting tools

As far as (free) symbolic debuggers goes: ddd and ups are currently the best ones with GUIs. For a non-GUI debugger, gdb is pretty good. adb (non-GUI) is lousy, and even the hardcore oldtimer admins don't bother with it much anymore. dbx (non-GUI) is ok, but you could skip it without regret. xdbx and xxgdb are ok, but ups and ddd are quite noticeably nicer. ups has a little nicer interface than ddd, but doesn't support as many languages.

Mail reading program (MUA)

Use netscape mail, or pine, or mh (mh-e, exmh), or Mutt, or one of the many (other) gui-based mail-readers. Don't bother with /bin/mail or mailx, or those other old clunky things. I personally use mhmail for sending mail from scripts, and netscape for reading - because it does mime nicely.

Mail transporting program (MTA)

There's sendmail, smail, qmail, exim and VMailer, Postfix - maybe others.

Window managers - the thing that gives window borders, popup menus in the background (wallpaper), and sometimes a set of "virtual screens" navigated with a "panner" or "pager".

There is a lot of these... Suffice to say that twm is horribly cramped (no virtual), and I like fvwm2. Windows users may like the feel of fvwm95. I've run into a number of AfterStep (the NeXT feel) and Enlightenment fans. Oh, and there's always CDE (dtwm).

Printers

Skip serial printing if you can: It's slow, and it's sometimes pretty painful to configure. Parallel printers are medium-speed, and not nearly as fussy as serial. Ethernet printers are good (fast and pretty easy), tho we often end up queuing all jobs through a unix host for preprocessing, prior to sending the jobs on to the network-enabled printer.
Among network-enabled printers, common protocols seem to be lpd (the standard stuff), EtherTalk (addressable from unix with CAP or Netatalk), and jetdirect (on HP printers). We tend to recommend Apple printers. The lpd functionality in HP printers is somewhat broken, and officially unsupported by HP.