This article is from the misc.writing Writing FAQ, by Wendy Chatley Green firstname.lastname@example.org with numerous contributions by others.
Go to the library and read the current _Writer's
Market_ published by Writer's Digest Books. It will tell
you which magazines and books are reading unsolicited
submissions, and what types of manuscript each market is
particularly eager for.
There are some good on-line site--check the
misc.writing home page (http://www.scalar.com/mw) for
current pointers to them.
When you investigate a possible market, don't just
read *about* it. Read other books printed by the same
publisher; read previous issues of the magazine. What the
editor honestly believes is "ground breaking, no taboos" may
be closer to "50's pulp fiction with swear words."
Be precise in copying the editor's name, title, and
address. Check them against the latest information you have
available. Editors change publishing houses and magazines
frequently; they are not terribly amused by receiving
submissions addressed to their predecessors.