Ancient to Early Medieval Bi-metallics  
   A quick review of early bi-metallic coinage.
   http://www.coinmall.com/CSNA/anc.htm

Bi-metallics Coins, Tokens  
   Includes articles on the subject, and some images.
   http://www.wbcc.fsnet.co.uk/sub003.htm

Encased Coins of Earl Fankhauser  
   Encased coins are a variety of bi-metallics. Learn about 'The Penny Man'-- Earl Fankhauser -- the most prolific maker of encased coins in history.
   http://www.geocities.com/Paris/Metro/5095/index.html

Joel Anderson: World coins  
   An offering of world coins and paper money and associated catalogs. Interesting list of bi-metallic coins for sale, with some scans.
   http://www.joelscoins.com/

W.B.C.C.  
   Online site of the Worldwide Bi-metallic Collectors Club, created to pool information about this type of coin. Includes catalogue, an image gallery, and all the club's newsletters.
   http://wbcc-online.com/