Carrot Cake in OC
Actually, the carrot cake at the Albertson's market deli is really good. Go buy a single serving and see if you agree.
There are so many styles of carrot cake, it's hard to narrow down one for you. If you want over-the-top spices and ingredients, try "Let Them Eat Cake" in Costa Mesa. They have samples. I don't prefer it, but everone's tastes are different.
And, Susie's Cakes in Costa Mesa has really good carrot cake.