Links to British
Terms and Slang:

These links will take you directly to the site
and will open in a new window.

In my opinion, the best source of Brit slang definitions on the web.

The American's guide to speaking British.

The American/British
British/American Dictionary
Exactly what it says.

MORE GUIDELINES FOR AMERICANS
Lots of interesting info here, from language and geography to culture.

The History of Swearing
in the UK
An amusing parody site from The Laughing Policeman Wireless
Society.  I included this site simply because it makes me laugh!

BritSpeak
Welcome to the BritSpeak Dictionary! Many of the words
you will find here are colloquialisms, the colourful language of daily living.

Not the same site as above.  The following description is off the site:
And You Thought You Knew English!
BrtiSpeak - An almost totally useless dictionary of
British English words and phrases and their American
English counterparts and meanings for your
reading and chuckling pleasure.