Paying members, read: http://support.polldaddy.com/cancel-payment-subscription/
Since PollDaddy works with your WordPress account, you may want to revoke access from WordPress. By the way, also check the WordPress entry on AK: it probably still cannot be deleted.
Deleting your account in PollDaddy: simply click the Delete Account button (when logged in, of course). Als see: http://support.polldaddy.com/my-account/