Chesscafe.com is certainly one of the best chess sites on the internet. This free site contains a lot of very interesting columns, chess lessons and puzzles.
My favorite columns are The Kibitzer by Tim Harding and The Instructor by Mark Dvoretsky, but I also like The Openings Explained by Abby Marshall very much.
Don’t forget to check out the Archives. Here you can find and download all the articles, reviews and endgame studies that have appeared at ChessCafe.com.