Even before the interactive command line editor of tcsh (and other unofficial versions of csh and zsh and bash and others) existed, csh had command line editing based on a line editor paradigm. This facility still exists today in almost all of the "modern" shells, and is worth learning. It's often a lot faster to type in a correction or modification to a command than to edit it appropriately!

Here I'll try to summarise some of the idioms I commonly use.

!!

As N-wing already noded, this just expands to the last command.

!abc

Expands to the last command starting with "abc".

!123

Expands to command #123 in the history list.

!abc:4

Expands to word 4 of the last command starting with "abc". Words are counted from 0, so !abc:0 is that line's command, and !abc:3 is its third parameter.

!!:$ or !$

Expands to the last word of the last command. Often used in idioms like this:

   % some_tricky_command prm1 prm2 ... > /long/path/to/output
   % grep 'regexp' !$
   % more !$

!abc:s/pattern/replacement

Expands to the last command starting with "abc", with the first occurrence of pattern replaced by replacement. pattern is unfortunately not a regexp.

^wrong^right

Short for !:s/wrong/right.

!abc:gs/pattern/replacement

Expands to the last command starting with "abc", with all occurrences of pattern replaced by replacement.

Teach your fingers to type these in automatically. It's a great way to semi-automate many tedious command-line tasks.