Bridge Base - Bridge Conventions
Conventions and the judgment to make them work by Mike Lawrence.

Paul's Bridge Site - My Bridge Stuff
Offers bridge games analysis and discussion on bidding topics; variations on existing and proposed new conventions; summary bidding guidelines and charts.

MSN Gaming Zone - Roman Keycard Blackwood
One of the oldest bidding conventions in Bridge is the Blackwood Convention. Join Fred Gitelman as he explores the convention and shows how it can work for you in online gameplay.