While it pays off to have an elevated status in the hotel chain, sometimes it makes sense to book stays with one of the third-party agencies, even though you may lose membership perks and get no points collected. In some cases the reason can be a lot lower price, in others lower price and free upgrades (if available). There are credit cards offering upgrades via partnership agreements, as well as third-party agencies. Here is the list which gets updated once in a while.
Most following services offer free upgrades, free breakfast, free wi-fi, late checkouts, hotel credits and other perks.
Luxury Hotel & Resort Collection by Chase. You need to have one of these cards: Sapphire Reserve Sapphire Preferred, Ink Business Cash, Ink Business Preferred, United MileagePlus Explorer, United MileagePlus Club, Freedom, Freedom Unlimited. More than 900 hotels.
Signature Luxury Hotel Collection by Visa offers similar perks. Sometimes includes a free night with 3-5 night stay. Any Visa Signature card will do. More than 900 hotels.
Travel & Lifestyle Services by MasterCard. Same perks. World or World Elite MasterCard is needed. More than 2000 hotels.
Fine Hotels & Resorts by American Express for Platinum Card owners. More than 1000 hotels.
The Hotel Collection by American Express for Gold and Platinum cardholders. No free breakfast or wi-fi.
Third Party Agencies
Virtuoso – Service offering various perks including free nights and upgrades in many hotels via advisors or simply online. Sometimes instant upgrades. More than 1100 hotels.
Signature Travel Network – Same as above. Sometimes instant upgrades.
Preferred Hotels – Multiple offers, including upgrades, early check in/out, free internet, etc. Also shows AmEx, MC and Visa free n-th night offers.
Tablet Plus by Tablet Hotels (curated by Michelin) – $99/year membership.
Leaders Club by Leading Hotels of the World – $175/year, includes annual pre-arrival upgrade.