I need any idea or wordpress plugin suggestion for user registration.
Users will sign up and site will generate a username and password which will be emailed to user. New users must submit the customer number of who referred them in order to complete the sign up process without any commission process.
ie., user must enter email address and referral id to signup and should get email of auto generated username and password.
Is there any idea for user registration with these process?
Your best option is Gravity Forms + Gravity Forms user registration.
You can create a form that includes a field for the referral and then with code you can check if the referral is correct or not not and based upon that results the user is created.
S2Member doesn’t have this capability.
S2member plugin may fulfil your needs I suppose http://wordpress.org/plugins/s2member/.