These are the 6 articles I wrote for the ACBL Bulletin on Doubles (in order of difficulty):
A double to show the other suits Takeout Doubles
Responder's double for takeout Negative Doubles
A double for takeout by the partner of an overcaller or takeout doubler Responsive Doubles
Opener's double to show 3-card support Support Doubles
Lead-directing, Maximal and other Doubles
You might also consider getting Larry's book on Doubles and Redoubles HERE or try Michael's Doubles Webinar which you can find HERE.