Does anyone know the secret to baking a light, moist cake from scratch? I have tried everything I can think of...ingredients at room temperature, checked the oven temperature, I'm not over mixing, I sift the dry ingredients 6 times, I temper the batter, and I've tried tons of different recipes, but every cake turns out very heavy and dense like a pound cake.
I sure would appreciate some help.

what type of cake are you making?

I like the recipe for white and chocolate in Elisa Strauss' Confetti Cake Book. Her red velvet cake recipe is very good also.

Try creaming the butter and sugar a little longer. That should help.

One more vote for Elisa Strauss' red velvet. I love that one. Her banana cake is delicious too.

I also love this one from Alisa Huntsman:

Vanilla Buttermilk Cake
http://smittenkitchen.com/2008/07/project-wedding-cake-the-cake-is-baked/
Scroll down. Very light and moist, don't overmix! It should take about 4 minutes to mix.

From same book:

Chocolate Sour Cream Cake
http://smittenkitchen.com/2008/08/chocolate-peanut-butter-cake/
Haven't made the frosting, but the cake is one of the best chocolate cakes I've ever had. It also mixes in one bowl, and if you don't want to, you don't have to use a mixer.

Temper the batter, meaning?