International Society of Genetic Genealogy (ISOGG)

There is a wealth of information available at the website of ISOGG, and membership is free.

Before You Buy - Check out these tips from ISOGG before you consider testing

Beginners Guide - links to blogs and articles for newbies

Testing Comparison Chart - comprehensive chart showing all the main testing companies and comparing the costs involved, the size of their databases, what happens to your DNA sample, and a wealth of other information that will help you to make an informed choice

DNA relationship charts - showing how much DNA is shared between relatives, which is invaluable for working out relationships between test matches