BlockFi (referral link) provides the BlockFi Interest Account which pays interest on crypto deposits. I received a promotion which provides you and the referrer with $50 worth of bitcoin each as bonus for signing up between September 23, 2019 and September 30, 2019.
To receive the offer, simply sign up with this referral link and make your first deposit before September 30, 2019. Make sure the referral code of 4a5cfc70 is entered when you are signing up.
It looks like the bonus will be paid out with the October interest payment. These are the promotion terms I received from BlockFi:
Offer valid until 11:59 PM UTC on September 30, 2019. Referrals must have had a balance of 0 on August 31, 2019 and must maintain a >0 balance through September 30, 2019. Referrals must be first-time BlockFi users that have never had a balance with BlockFi.