I haven't read the threads here for Brownie recipes but I'm sure they beat out my suggestion hands down, knowing the talented members here.
But with that being said, my favorite is found on the back of some (not all) Hershey's Cocoa Cans (unsweetened powder). I haven't made them in eons but when I did I usually used an 9X12 pan (so the corners wouldn't dry out) and cooked them a little longer...or I doubled the recipe and put in a 13X9X2. I'd cook them maybe 45-50 minutes instead of the recommended 30-35 minutes because of the smaller pan size...until the toothpick in center was clean (a few crumbs is okay). Here is their link with the recipe. I never iced them....sweet enough as is:
HERSHEY'S Kitchens: Recipes: HERSHEY'S Best Brownies
(They also have the best fudge recipe on the back of some cans)