paralist package provides compressed lists, the new environments are called
compactdesc. Use it just like the corresponding standard list environments. It can even keep lists within a paragraph.
enumitem provides more features but also compressed lists, for instance by
\setlist modifies all lists,
itemize etc. It takes an optional parameter that stands for the level that should be changed, default it alters all levels. Since
enumitem allows a lot more customization I prefer it over
paralist, but the latter is easier to use and fits better to the question here.