Betty Crocker has a great site with things to do with store bought brownie mix. Things you can mix in, ways to decorate brownies, unique ways to serve them ( like on a stick, Popsicle style), and more. Check out the link for inspiration.
Here a very easy way to make a pan of brownies look more special from my friend Candice. Let them cool and then frost them with a thin layer of cream cheese frosting and then sprinkle chocolate chips on top of the frosting. You can also top with grated chocolate or sprinkles.
I've never made brownies from scratch, I think the mixes taste just fine. I think my favorite is the ALDI store brand mix and it is so cheap. Very moist brownies!
Enjoy your brownies!