You're trying to launch a product and you don't have anything to show for it... yet.
But, you want to build your email list.
My friend put it best, "you're trying to sell the sizzle before the steak."
Currently I'm in the process of growing my email list. My product? A wristwatch, that will, after prototyping, go to Indiegogo.
This problem isn't physical product specific, it could also apply to an info product, forum, service, etc.
Getting potential buyers to visualize and desire the product before they have an opportunity to peak into it's true value to them (i.e. seeing the watch, reading the first chapter of a book, seeing parts of a training course, etc.), seems more emotional than rational. Almost, as if you are selling the thought of life with your future product.
What kinds of things are you guys doing to sell the sizzle before the steak?
How do you bridge that emotional/rational gap when selling before you have a product?