Official Documents

The Document Library on the ACBL website is a good starting point for all official documents from convention charts to the law books as well as many other articles.
This very technical document contains information on how masterpoints are calculated.

Words from Experts Who Need No Introduction

Larry Cohen, Eddie Kantar, Robert Todd,  Marty Bergen, and Audrey Grant

Conventions

Practice conventions here at Baker Bridge
Huge library of conventions explained at Bridge Bums
If you are curious about popular conventions played elsewhere in the world, you can find a wide range of them here.

Tools

BBO offers many practice tools
The website by Thomas Andrews has a tool for hand evaluation and a lot of fascinating hands.

Publications and Podcasts

Almost 100 years old, Bridge World is probably the oldest bridge publication
Bridge Winners is a somewhat technical blog site for bridge players, with a weekly column by Kit Woolsey.
Sorry Partner is a podcast which features interviews of many bridge luminaries.