Jetsetter is a website (affiliated with Gilt) that features luxury hotels around the world at discounted prices. Granted, the costs are still expensive, but they make spa packages and penthouse suites and whatnot slightly more affordable. The dates are usually limited to some time within three or four months of the sale date so you can't really plan a vacation 1 year ahead and hope to book anything through them.

You have to sign up (there may be a waiting list) in order to participate in the sales. They send out emails with previews on what the upcoming sales are.

I have yet to book anything with Jetsetter, but I hope to find an opportunity (and the money) to be able to soon.