Since you're asking in this forum, I assume you're looking for a tried-and-true recipe, right? Sometimes the advice of someone who's tried and enjoyed a recipe carries more weight than a simple Google search.

I haven't tried any of the food52 recipes, though I have no doubt they're divine, same as all of the food52 recipes I've tried.. This happens to be my favorite recipe:

http://www.epicurious.com/recipes/food/views/Double-Chocolate-Layer-Cake-101275

you can check out all the chocolate cake recipes on the food52 recipe database:
http://www.food52.com/recipes/search?recipe_search=chocolate+cake&commit=Go

or a simple google search will give plenty of options.