Cooks Illustrated (Subscription Required)http://www.cooksillustrated.com
This is a great site for geeky cooks, their take on cooking is detailed and helpful, especialy for thoose of us that have not had much help in the kitchen. They do not take anything for granted, all steps are clearly explained. Most recipes are arrived at through a trail and error process that is explained in detail. This is my go to source when I am looking for a recipe that is going to come out great.
Rouxbe (Free for 30 days)
Updated June 6th, 2012: I have had nothing but problems related to their billing system, sending multiple notices and in my mind a confusing upgrade process. When I have sent them emails regarding my issues I have received emails that went out of their way to show how I was wrong in my assumptions. This did not leave me with a feeling that had any interest in actually having a two way conversation. I would NOT recommend this site at all.
Mark Bittman on Food (Blog)http://bitten.blogs.nytimes.com/
I found a reference to this blog on lifehacker. I find that Mark has an infectious style and although I am not quite ready to be as hardcore about some of his ideas, I find his recipes simple and delicious. We love the Seven-P recipe and we had is Welsh Rarebit (Rabit) for a new years day snack. He has cool video series of videos including one up with Jamie Oliver aka The Naked Chef where he cooks up a simple Parmesan Chicken.
This site has an active set of forums and has been a good resource for recipes of items that we do not have access to here. For example, I created a green bean casserole (Recipe from Cooks Illustrated) for Thanksgiving, but with no French's Onions to be had, I needed to make them from scratch... I found a recipe for them here.