I've generally found the Hideaway Report helpful though, as noted above, hardly exhaustive. I guess I'm particularly grateful for a terrific recommendation a few years ago for a travel agent in BA.
I don't always agree with their reviews (I've hated a couple of hotels they've lauded), but often find them useful.
I've been a Q Club member for a number of years. Though I'm not sure it's worth it, I have on occasion (more in the past than the present) found their deals better than the competition.
I scored a very good deal (offseason, but it suited my travel plans) on one e-auction; I had the impression, though, that ANYONE can bid, but perhaps that's incorrect.