One of the smartest things Product Hunt did, and many copied, was to add an email sign up box at the top of their page. They've since changed it. But it was smart as it gave them the ability to re-engage users.
So how should it look? Adding just "subscribe to my newsletter" sucks! It doesn't show people value. The last thing I want if I go to your site is to subscribe to another newsletter. Instead, give me something useful and customized:
For example, if you have a jobs board and I'm browsing the PHP jobs:
That's actually useful to me. Instead of thinking about how useful getting their email address is to you, think about what would be useful to a new user so that you can capture their email address.
For this we will have to show unavailable domains. this is the user can choose which domain they want to be notified for. We can discuss our options before implementation.
From Peter Levels