As an example to work with, here's mine.
RESET="\[\017\]"
NORMAL="\[\033[0m\]"
RED="\[\033[31;1m\]"
GREEN="\[\033[32;1m\]"
YELLOW="\[\033[33;1m\]"
BLUE="\[\033[34;1m\]"
WHITE="\[\033[37;1m\]"
SMILEY="${GREEN}:)${NORMAL}"
FROWNY="${RED}:(${NORMAL}"
SELECT="if [ \$? = 0 ]; then echo \"${SMILEY}\"; else echo \"${FROWNY}\"; fi"
# Throw it all together
PS1="${RESET}${GREEN}\u@\h${NORMAL} ${BLUE}\W \`${SELECT}\` ${GREEN}\$${NORMAL} "
What that does is give username@boxname in green. Directory in blue, and then either a green smiley if your last command exited with code 0 (succeeded), or a red frowny if it exited with non-zero (didn't succeed).
I don't remember offhand where I nabbed it from, but I added it because I was tired of always doing echo $? to see if some goofy command like named-checkconf exited with nonzero.