On PHPBuilder.com today Jason Gilmore has a new tutorial posted showing how to combine PHP, MySQL and a jQuery interface to create a newsletter subscription popup for your site that doesn't interfere with the flow of the site.
More recently, websites have taken a more aggressive approach in terms of inviting visitors to subscribe to a newsletter or consider some other special offer. The approach involves displaying a popup window the very first time a visitor navigates to the website. The visitor has the option of either responding to the offer or providing his e-mail address by interacting with the popup, or can choose to close the popup at which point it won't reappear for a (hopefully) significant period of time.
He uses two jQuery plugins - simplemodal and jquery-cookie to do some of the heavy lifting on the frontend. Full HTML, CSS and Javascript code are provided to make the interface work. There's no backend code for the PHP/MySQL integration, but it's a pretty simple form so it shouldn't be overly difficult.