http://wccftech.com/steam-sales-dates-revealed/

Until the end of the year, three more Steam sales will be held. While official dates have yet to be confirmed, we have learned precisely when they will begin and end, with the first one being quite close.

According to Kotaku UK, the next one of the first next three Steam Sales will begin next week, on October 26th, and last until November 1st. The other two sales will be held in late November and December, respectively.