Email Marketing for my Members Website.

I currently have a website based in PHP that has alot of members. When users sign up they get information gets stored in a MYSQL database...

i get members everyday pretty much signing up.... So i have a MYSQL database that is constantly filling up with new email addresses.... my question is how can i do email marketing?

i used to use aweber alot when i was just had basic opt in forms.

now i have usernames, companies, passwords, email addresses etc..

is there any emailing software that i can integrate? so that when people sign up to my website the software can just use the emails in the database?

I tried doing some aweber api stuff - when a user signs up to my website, information is passed to aweber.. but that is not working out to well...

any suggestions?

Thanks