LaunchRock - Perhaps the Quickest and Most Popular Way
If you're looking for the easiest way to set up a launch page, this is probably it. This is completely free, and is pretty flexible. You can host it on a LaunchRock subdomain (e.g. yourapp.launchrock.co) or you can purchase a domain (through LaunchRock or map your own domain) to host the LaunchRock page. This app gives you the ability to set up an email capture and collect stats and info.