Tie Accounts to Email

My suggestion would be to require all future accounts to require an email verification before they can begin posting. This is a simple, common, and non-obtrusive method of account activation. Then make it so that when an account is banned/suspended, all accounts using that same email are automatically banned/suspended. So banned users would have to make a new email every time they wanted to make a new account and go through verification again.

Before you came along that was already considered, and it was rejected because it too would not work, people can just use throw-away email addresses to come back.

Yes, but it takes more effort and time wasted on their part. Basically, just make the process as painful as possible for offenders, without having any real effect on the normal community.