Smart Email Field is a js plugin that can autocomplete email addresses. When you start typing your email, and hit the
@ symbol, it starts offering common email domains to autocomplete.
You can apply it to any input field, and it will use those custom styles and perfectly blend in with it.
I think it could be usefull if people started using it on their sites, but it does have a few issues that are yet to be solved. You can report an issue here.