Check out the Account Manager... it allows auto-expiration, auto-expiration with email reminders, credit card support for pay site, among a slew of other features.
Thanks however I don't really want to spend $300+ (AUD to US) on a program I intended to modify. Do you know where I could find some expiry date source code instead. I have already have written most of the membership database bar a few features this being one of them.
The Account Manager Lite (shareware) also has the account expiration feature. I didn't find any other membership manager program (or code) for expirations.