Starwood Preferred Guest
Between September 12, 2017, and January 15, 2018, earn 1,000 bonus Starpoints per stay at St. Regis, The Luxury Collection, W, Le Méridien, Westin, Sheraton, Tribute Portfolio and Design Hotels properties, 500 bonus Starpoints per stay at Aloft, ElementS and Four Points properties, and 10,000 bonus Starpoints when you stay 25 or more nights. Register here by November 30, 2017.
Check here to see if you're targeted for a promotion running between September 15 and December 15, 2017. Offers include double elite qualifying stays and nights and bonus points after a certain number of paid nights, and potentially others.
Between September 1 and October 15, 2017, receive a 20% bonus on the total number of AAdvantage miles received for Starpoint transfers to American Airlines (i.e. after the 5,000-point bonus for transfers in increments of 20,000 Starpoints), plus 10,000 AAdvantage miles for every 100,000 AAdvantage miles received from conversions. Transfer in multiples of 80,000 Starpoints to maximize the promotion, although see here for a potentially better option involving Marriott Hotel + Air packages.
If you have a co-branded Hilton American Express card check your Amex Offers to add an offer of $50 back when you spend $250 or more at participating Hilton Hotels & Resorts properties.
Between September 1 and December 31, 2017, earn double base points on all paid stays. Diamond members also receive 10,000 points for every 10 nights during the promotional period. Register for the promotion here.
Between September 15, 2017, and January 15, 2018, earn a free night that can be redeemed at category 1-5 properties after completing two paid stays, and unlock additional offers depending on your Marriott Rewards elite status. Register for the promotion here by November 30.
World of Hyatt
Chase World of Hyatt credit cardholders can stay 10 qualifying nights between September 1 and December 30, 2017, to receive Explorist status for 2018, or 20 qualifying nights to receive Globalist status for 2018. Register here by September 30, 2017.
The last global World of Hyatt promotion ended June 30, 2017, and the next one hasn't been announced yet.
IHG Rewards Club
Between September 1 and December 31, 2017, register for the IHG Rewards Club Accelerate promotion and complete the offers you've been targeted for to receive bonus points. Register for the promotion here.
Here's the list of current IHG PointsBreaks properties, for reservations made through October 31, 2017.
Between July 1 and September 30, 2017, for every two stays you complete you'll earn a free Friday stay certificate or 10,000 Gold Points, up to 3 Friday stay certificates or 30,000 Gold Points. Free Friday stays can be redeemed between October 6, 2017, and January 26, 2018. Register for the promotion and select your preferred reward here.