I've been making the 'Betty Crocker' cakes and cupcakes (I love that they come with frosting for you) and they are the most moist cakes I have every made and pretty easy to make with just adding water, eggs and oil/butter (depending on what you are making).

I made the cake for DD's birthday party and it lasted for a few days without going stale and the cupcakes don't last too long when they are made