Trader Joes sells a fat free brownie mix (that is friggin delish) that uses yogurt so if you live near one hit them up.
Here is a link to another yogurt brownie recipe
quick-brownies recipe from FatFree
Haven't tried this one yet
here is another recipe
2-1/4 cups all-purpose flour
1/2-1/3 cup cocoa (baking cocoa)
1/4 cup artificial sweetener
1 tsp. baking powder
1/4 tsp. salt
1 cup spring water or 100% apple juice
1/2 jar mashed carrots baby food
Directions:
Mix dry ingredients together. Slowly stir in baby food and water or juice. Let sit 10 minutes then put into 9x10-inch pan. Cook in 350°F oven for 1 hour.