BetaList is the place to list your Startup before you publically launch it, or before you even start building it. Submit for free and wait two months to be listed, or pull the trigger and spend $99 to get listed in a couple days. If your service is something that resonates with their (mostly Startup focused) audience, you can get a ton of people on your list very quickly. This is where we got all of our pre-launch traction for StartupResources, gathering about 500 people on a list in two weeks before we put the site live.