TripAlertz.com offers hotel deals that get cheaper as more people buy them.
What's hot: This private-sale member website is free to join. Click on "View Deal" to see the Trip Alertz sale price and the lower "Epic Price" that the site will offer after a certain number of bookings. When enough people book, you'll get the lower price; otherwise, you still get the original deal. Cancel or change your reservation up to 15 days before the date for a $25 fee; after that, the website won't accept changes.
What's not: Not enough variety in the destinations, and prices not always the lowest.