There are many gay-friendly hotels in Frankfurt most of them right in the center of the gay "Bermuda Triangle" district, for example, 
Hotel Scala and 
Villa Orange. The 
Downtown Hotel Frankfurt is also a gay-friendly hotel centrally located at the heart of the city's gay scene. In the same building you'll find the popular bar/café Lucky's LM 27.
Hotel reservation: 
Tel.: +49-(0)69-21 23 08 08
Fax: +49-(0)69-21 24 05 12
Online-Reservation: 
Frankfurt Tourism Information