Epicurious is easily one of my favorite cooking sites. There are thousands of different recipes to choose from. Each recipe has reviews left by people who have tried the recipe and they often offer tips to improve the recipe. Sometimes I use the site when I have some ingredients that I would like to use--for instance, I had a lot of zucchini and some fresh salmon, so I typed those terms into the search feature and all of a sudden I had several recipes that used both zucchini and salmon. The same concept works if you had something you really liked at a restaurant and want to make something similar at home. Additionally, the site allows you to browse recipes by category (e.g. "healthy" or "quick & easy"). I also love some of the tools such as the Food Dictionary and the Wine Pairing resource.
There is also a great app for Android users (and probably iPhone too) that I find really useful. You can use the Epicurious App to pull up recipes while you are cooking rather than printing them out or even worse, dragging your laptop into the kitchen. You can also add recipes to a "shopping list" or pull up the recipe at the grocery store if you are questioning whether you have something. I can't say enough good things about this website (and the smartphone application). It has been a wonderful tool during my cooking adventures.