IHG Rewards Club has an “Anniversary Bonus Offer” promotion for 1,000 bonus points for one stay within 90 days of registration.
Note that this offer is from 2013. I can confirm, however, that it is still valid if you have not done it previously.
You can earn this 1,000 bonus points once and need to do it within 90 days after registering for this promotion.
Note that this offer is combinable with all the other IHG Rewards Club promotions that you can find here.
You should sign up for this promotion when you know for sure that you have a paid stay coming up within 90 days. The expiry date of this offer is unclear.
This very same offer in 2013 yielded 1,000 bonus points per stays for 60 or 90 days. In 2014, however, the bonus offer is valid just for one stay.