Drifter

As far as I know, none of mine are gay owned, but all are definitely gay-friendly.
There's a new restaurant on Soi Yen Akat (about 400 meters from the Malaysia Hotel) called Workshop. Intimate, mid-price but great food and service. At least one of the staff came from Zanotti in Soi Saldaeng. Portions may be on the smallish side if you are desperately hungry!
Il Bolognaise at the end of the short Sathorn Soi 7 (the Singapore Embassy is on the corner of Sathorn and Sathorn Soi 7). Been around quite a few years, excellent Italian food at reasonable prices.
Near the top end of the price scale, Eat Me off Soi Convent has consistently been wonderful for probably around 20 years. Great atmosphere, impeccable friendly service, Australian fusion menu, several wines by the glass selections - and fabulous desserts!
For a small coffee shop with a small menu of excellent food and again excellent service, Kush on Soi Nanglinchee has become a favourite. For breakfast or brunch, their scrambled eggs with melted cheese, bacon, salad and the largest and best croissant you will find in the city is superb. Nanglinchee is the extension of Soi Suan Plu off Sathorn. Kush is on the right just before the gas station on the opposite side.
For Thai food, it takes a lot to beat Ruen Urai. This is set in a Thai House in the grounds of the Rose Hotel off Suriwong. This s nothing like the hotel itself. The quality is really excellent and the atmosphere almost unbeatable. However, always book ahead and ask to be seated on the ground floor. The upper floor is boring! Mid-price.
The only restaurant that I have ever found gay un-friendly was Indigo off the Silom end of Soi Convent. French cuisine, mid-price and patronised by many of the French community. The owner was a total homophobe who would rant about the gay Fan Club massage being just across the soi until it closed some years ago. I believe it is now run by his son, but after one of his rants 6 years or so ago, I vowed not to return.