Does anyone happen to have any decent mailer scripts they can recommend?

What we're looking to do is this..

Have say, 10 individual niche specific pages on 10 different domain names each having an email collection box on it.

When a surfer enters their email address and clicks the 'subscribe' button, that email address gets entered into a specific niche list of email addresses however, if possible, we dont want the surfer to leave the page they are on when they submit their email addie.

Also, in the administrative side of the script, we should be able to mail the lists on an individual niche basis and, if possible, collectively across all niches.

So does anyone know if such a script (php based preferred) exists?

Regards,

Lee