What useful things can one add to one's .bashrc? [closed]

I have a little script that extracts archives, I found it somewhere on the net:

extract () {
   if [ -f $1 ] ; then
       case $1 in
           *.tar.bz2)   tar xvjf $1    ;;
           *.tar.gz)    tar xvzf $1    ;;
           *.bz2)       bunzip2 $1     ;;
           *.rar)       unrar x $1       ;;
           *.gz)        gunzip $1      ;;
           *.tar)       tar xvf $1     ;;
           *.tbz2)      tar xvjf $1    ;;
           *.tgz)       tar xvzf $1    ;;
           *.zip)       unzip $1       ;;
           *.Z)         uncompress $1  ;;
           *.7z)        7z x $1        ;;
           *)           echo "don't know how to extract '$1'..." ;;
       esac
   else
       echo "'$1' is not a valid file!"
   fi
 }

Since I use so many different machines, my .bashrc always sets the command prompt to include, among other things, the name of the server I am currently logged into. This way, when I am three levels deep in telnet/ssh, I don't type the wrong thing in the wrong window. It really sucks to rm -rf . in the wrong window! (Note: At home, telnet is disabled on all machines. At work, ssh is not always enabled and I don't have root access to very many machines.)

I have a script ~/bin/setprompt that is executed by my .bashrc, which contains:

RESET="\[\017\]"
NORMAL="\[\033[0m\]"
RED="\[\033[31;1m\]"
YELLOW="\[\033[33;1m\]"
WHITE="\[\033[37;1m\]"
SMILEY="${WHITE}:)${NORMAL}"
FROWNY="${RED}:(${NORMAL}"
SELECT="if [ \$? = 0 ]; then echo \"${SMILEY}\"; else echo \"${FROWNY}\"; fi"

# Throw it all together 
PS1="${RESET}${YELLOW}\h${NORMAL} \`${SELECT}\` ${YELLOW}>${NORMAL} "

This script sets the prompt to the host name followed by :) if the last command was successful and :( if the last command failed.