Any suggestions for a luxury hotel in Prague that is worth the money?

Four Seasons, Renaissance and Hilton are all generally reliable. If they're worth it depends on how much you're paying - and how much the cost matters to you.

A recent poster was raving about the Alchymist.

www.alchymisthotel.com.

I would definitely recommend staying at a hotel within a reasonable walking distance to the Old Town Square (Prague 1). I stayed at the Marriott which was very nice and a short walk to the town square.

In addition to the FS, there's Mandarin Oriental and -- possibly the value leader for the luxury hotels there -- Hotel Le Palais Prage.

When are you travelling?
We are going to Prague mid-November, and after a great deal of research have settled on the Alchymist Grand Hotel and Spa. Looks like it is full of atmosphere (maybe a bit OTT, but in a fun way), good size rooms, gets very good reviews on TripAdvisor, and they have responded to my many emails and queries promptly.
If you can wait till then, I will post a review when I return to the land of Oz.