I don't know of specifically gay hotels in central London--maybe a few in Earls Court but not near Soho. Not sure what your budget is (it's all relative), but last time I paid for a hotel when I was in London I booked through the website londontown.com. They have a section called "top secret hotels" which will tell you the hotel's location and amenities but not the name until you've paid--this is done by hotels to preserve their brand image while still filling rooms. I ended up in a 5-star hotel for about a hundred dollars a night, and it was in Oxford Circus (a half mile from Soho Square).
Radisson Edwardian is a good chain, and they have 2 locations on the edge of Soho: one in Leicester Square and one in Seven Dials (where Covent Garden meets Soho). Rather than searching for hotels in Soho you're better off searching the locations called Covent Garden, Leicester Square, and Bloomsbury (British Museum area). I'm happy to give advice if you see any specific hotels that seem like a good deal.