The Healthy mummy has some great healthy cake recipes. Maybe join their facebook page. They often post free recipes on there.

Replace sugar with banana or dates or maple syrup. Replace butter with coconut or olive oil. And cook a vegetable cake, that’s about as healthy as you’ll get a cake

It’s a bigot a cheat but there is some great cake mixes these days ,Greens is a good brand .

there are some healthy cake recipes on this site which look good. otherwise taste.com have some great recipes there too.