I write in the period from about 1900 to 1940 or so, so I have to be very careful of my slang, because some of the folks who might be reading my work might still be alive.

I recommend it constantly, but if you don't have one yet, get a Cassell's Slang Dictionary. It's a honking doorstop, but worth its weight in a precious metal of some sort:

http://books.google.ca/books/about/C...AC&redir_esc=y

It's got West Indies, Australia, UK, the States, South Africa, etc, and groups the words by century (for the more historical stuff) or by decade for the more modern stuff.

Hip says four stars!