The enumerate package allows you to control the display of
the enumeration counter. The package adds an optional parameter to
the enumerate environment, which is used to specify the
layout of the labels. The layout parameter contains an enumeration
type ('1' for arabic numerals, 'a' or 'A'
for alphabetic enumeration, and 'i' or 'I' for Roman
numberals), and things to act as decoration of the enumeration. So,
for example
\usepackage{enumerate}
...
\begin{enumerate}[(a)]
\item ... ...
\end{enumerate}
starts a list whose labels run (a), (b), (c), ...; while
\usepackage{enumerate}
...
\begin{enumerate}[I/]
\item ... ...
\end{enumerate}
starts a list whose labels run I/, II/, III/, ...
The paralist package, whose primary purpose is
compaction of lists, provides the same facilities
for its enumerate-like environments.
If you need non-stereotyped designs, the enumitem package gives you most of the flexibility you might want to design your own. The silly roman example above could be achieved by:
\usepackage{enumitem}
...
\begin{enumerate}[label=\Roman{*}/]
\item ... ...
\end{enumerate}
Note that the '*' in the key value stands for the list
counter at this level. You can also manipulate the format of
references to list item labels:
\usepackage{enumitem}
...
\begin{enumerate}[label=\Roman{*}/, ref=(\roman{*})]
\item ... ...
\end{enumerate}
to make references to the list items format appear as (i), (ii),
(iii), etc.
The memoir class includes functions that match those in the
enumerate package, and has similar functionality for
itemize lists.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=enumerate