Instead of running:

$ ls -lh `which zsh`

use this:

$ ls -l =zsh

To have zsh automatically cd to a directory without requiring you to type cd, set this option:

setopt auto_cd

So, if you have a directory foo in the current directory (and no command foo exists in your path), typing simply foo will be equivalent to cd foo.

To have zsh autoload functions, you can place them in a directory and have zsh search the path when the functions are called. For example, consider a function foo defined in ~/functions/foo. In your ~/.zshrc add:

FPATH=~/functions:$FPATH
autoload foo

Then, whenever you call foo, zsh will attempt to read ~/functions/foo for the function definition. To reload a function after you have changed its source file, run:

unfunction foo
autoload foo

The next invocation of the function will cause a reload of ~/functions/foo.

You can edit an environment variable in-place by running vared:

$ vared PATH

It will give you a readline-style buffer to edit the variable's contents and will save them back to the environment after you're done.

Some examples of useful file globbing supported by Zsh (if setopt extendedglob has been run):

$ ls foo<1-100>
  (Lists files 'foo1', 'foo2', ..., 'foo100')
$ ls foo<-50>
  (Lists files up to 'foo50')
$ ls *.c~foo.c
  (Lists all *.c files except foo.c)
$ ls *.php~foo*(.)
  (Lists all plain *.php files except those starting with 'foo')

You can complete man page names as well as file names. Put these lines in your ~/.zshrc:

setopt SH_WORD_SPLIT
function man_var () {
   man_pages=( /usr/share/man*/*(N:t:r:r) )
   compctl -k man_pages man
   reply=( $man_pages )
}
compctl -K man_var man; man_pages=()

Now type man foo and the hit TAB to get a list of all man pages beginning with foo.

(Note: this tip taken essentially verbatim [after testing and fixing] from http://www.unixtips.org/index.php3?catList=30.)

If you pipe the output of command into command like less or grep often, a global alias can save you a number of characters to type:

$ alias -g G='| grep'
$ alias -g L='| less'

so that this command:

$ ls * | grep foo | less

becomes:

$ ls * G foo L

(Note: This tip taken essentially verbatim from http://www.unixtips.org/index.php3?catList=30.)

Zsh can run a command and let you do things with a temporary file with the resulting output:

$ emacs -nw =(ps aux)

This will create a temporary file with the output of ps aux and let you edit it in Emacs. Or:

$ diff =(ls) =(ls -F)

Will run diff on the output of the two commands.

If you use pushd and popd to maintain your directory stack, then ~N (where ~0 is the top of the stack) will expand to the appropriate directory in the stack. For example:

cygnus:~$ pushd usr
~/usr ~
cygnus:~/usr$ pushd /etc
/etc ~/usr ~
cygnus:/etc$ pushd /usr/lib
/usr/lib /etc ~/usr ~
cygnus:/usr/lib$ cd ~2
cygnus:~/usr$

Furthermore, you can make cd use pushd and popd functionality implicitly:

~> DIRSTACKSIZE=8
~> setopt autopushd pushdminus pushdsilent pushdtohome
~> alias dh='dirs -v'
~> cd /tmp
/tmp> cd /usr
/usr> cd bin
/usr/bin> cd ../pub
/usr/pub> dh
0       /usr/pub
1       /usr/bin
2       /usr
3       /tmp
4       ~
/usr/pub> cd -3
/tmp> dh
0       /tmp
1       /usr/pub
2       /usr/bin
3       /usr
4       ~
/tmp> ls =2/df
/usr/bin/df
/tmp> cd -4
~>

(Note: The text above is taken essentially verbatim from http://www.b2pi.com/zsh/Intro/intro_6.html.)

Sometimes you need to iterate over variable names and access their values. In shell script, you would do something like this to get the values of FOO and BAR:

$ FOO=apple
$ BAR=orange
$ VARS="FOO BAR"
$ for v in $VARS ; do echo ${!v} ; done

The above works in bash. Use this in Zsh:

$ for v in $VARS ; do echo ${(P)v} ; done

(The 'P' flag on ${v} causes a further variable lookup before ${v} is evaluated.)

Thanks to Cliff for the tip!