Today there is a flash sale over at IHG where you can claim reward nights for between 25%-75% off their normal rate. Don't forget that you do not pay cash for these rates, these are paid in points! And also it's for stays from 8th October – 8th November 2013. I don't know at what time of the day this begins, so be prepared for it to start any time of the day.
The list of participating hotels was announced in a preview a few days ago by a “community manager” on IHG's own forum. I've only ever stayed at one of the hotels — the Holiday Inn Express Los Angeles – LAX airport — and it was perfectly acceptable for an overnight transfer at LAX. Probably not much more though!
Once the live link appears I'll update this post to include it.