mailing list managers

Hi all, Just a quick note to see if anyone has any experience with mailing list managers. I've currently got a DB of subscribers, and basic PHP scripts are not going to be a good long-term solution. I was hoping that maybe there's an opensource or commercial product out there that I can install in my doc root (ie, PHP + MySQL support) which will handle this in a more effective manner (ie, space the mailout across an hour or so, etc etc). Or alternatively, somebody might recommend a service such as sparklist.com (but cheaper, since they're targeting a list with greater numbers @ a minimum of $50/month). TIA, Justin French