Below is a list of guest friendly hotels in Thailand. Most of these can be booked through ThaiHotelDiscounts.com.
When booking please mention Thai360 to get a discount and to provide this board with a slight commission.

For those unfamiliar with the term, guest friendly hotels are those hotels that do not object to their guests taking visitors to their room for the night.

Bangkok

• Bangkok Boutique
• Centre Point Group
• Citi Chic Hotel
• Conrad Hotel
• Davis Hotel
• Dynasty Inn
• Dynasty Grande
• Euro Grande
• Federal Hotel
• Grace Hotel
• Grand Business Inn
• Grand President
• JW Marriott
• Landmark
• Majestic Suites
• Majestic Grande
• Manhattan Hotel
• Nai Lert Park
• Nana Hotel
• Novotel Lotus
• Palazzo
• Pinnacle Lumpinee
• President Park
• President Solitaire
• Rembrandt Towers & Serviced Apartments
• Royal Ivory Nana
• Royal President
• Sheraton
• Stable Lodge
• Swiss Grottino
• Swiss Park (need to book twin/double)
• The Oriental
• The Regency
• Town Lodge
• Westin Grande
• White Orchid

Pattaya

The vast majority of hotels in Pattaya are guest-friendly, but here's a list of confirmed hotels anyway.

• Green Park Resort
• Hard Rock (but only if booked direct)
• Marriott
• Penthouse
• Pig and Whistle (book ahead)
• Sunshine Hotel and residences

Hua Hin

• City Beach Hotel
• Hilton
• Jedpeenong
• Peony
• PP Hotel
• PP Villa
• Most Guesthouses
• Subhamitra Hotel

If you are aware of any hotels that are not on this list - or that are, but shouldn't be - please let me know at sanuk@thai360.com