Save on your next hotel booking with these useful online services

But Eisen reserved her room at the all-inclusive Sanctuary Cap Cana in the Dominican Republic through a new travel site, Tingo.com. Each day, the booking site automatically checked to see if the hotel lowered its price for the nights Eisen was staying there. Eventually, the price fell. Tingo canceled Eisen's original reservation and rebooked her at the new, lower rate. Her savings: $1,874.

"I would not have considered that you could continue to ask: Are there any discounts? Are there any discounts? Are there any discounts?" said the Wynnewood, Pennsylvania, psychologist. "I don't think most people would. You book it and think this is the best price I can get."

Tingo is one of a growing number of services that aim to save travelers money on their hotel stays.

The site, which is owned by TripAdvisor, says that travelers have a 20 percent chance of getting at least some money back. The typical rebate is $50, according to the company, but occasionally travelers like Eisen get much more back.

The site requires prepayment of the room and focuses on fully refundable rates. Sometimes, cheaper rooms might be available through other booking channels but they typically can't be canceled.

Tingo isn't the only site changing the way travelers book. A host of new apps are offering steep discounts on hotel stays, particularly last-minute bookings.

HotelTonight offers discounted rooms at more than 2,000 hotels via its iPhone and Androids apps. Each day at noon local time, a slate of rooms is released for each of the 80 cities it currently serves. There are luxury hotels, hip hotels and those categorized as "solid" or "basic."

The savings can be substantial.

A recent search turned up the Bryant Park Hotel in New York. HotelTonight said a room there should cost $345 but was offering it for $239. (A check of the hotel's own website showed $285 as the lowest rate.) Two hours later, the room was being offered for $199. Two hours after that, HotelTonight was out of rooms at the Bryant Park Hotel.

A search for Chicago turned up the Wyndham Blake Hotel. HotelTonight said the going rate was $179 but that it could offer a room for $129. The cheapest standard rate on the hotel's own website was $169; a room could be had for $152 for AAA members.

HotelTonight users can't request room types, so it is best used by solo travelers or couples. And while many hotels offer ample nonsmoking rooms, nothing is guaranteed using the app.

Travelers can book rooms until 2 a.m. - perfect for unexpected travel delays or those who might have partied too hard and just don't want to go home.

Rooms can be booked for up to five nights but check-in must occur the day of booking.

But as with all travel deals, make sure to shop around. Rates aren't always cheaper on these apps. For instance, HotelTonight was offering a room at Caesars Atlantic City for $49 a night, down from the regular rate of $62 for that night. However, a quick visit to the hotel's website found a room for $39 thanks to an online promotion that was being automatically applied to all bookings. As an added bonus, guests could pick a smoking or nonsmoking room.

Priceline - one of the original discount hotel sites - has also jumped into the same-day hotel sale frenzy.

Through its iPhone and Android apps and its mobile site, Priceline is now offering "Tonight-Only Deals." The service covers approximately 150 cities and towns around the U.S. on a typical evening. It only applied to three- and four-star hotels. Offers start to post at 11 a.m and rooms can be booked up until 11 p.m. local time, or until they sell out.

Unlike Priceline's traditional service where travelers bid on unknown hotels, Newyork0 the hotel names are displayed along with descriptions, maps, photos and customer satisfaction scores.

A recent search for a room in Memphis turned up the Madison Hotel. Priceline said the room should cost $242 but was offering it for $184. The hotel's own website was charging $242.

Sometimes, the deals through the Tonight Only specials of Priceline's mobile app are even better than Priceline's own website.

The Royal Sonesta Hotel in New Orleans had a room recently for $229 on its own website and Priceline.com. However, Priceline's mobile app had a Tonight Only offer of $183.

Priceline says Thursday night stays tend to deliver the deepest savings, while Sunday is the most popular check-in night among last-minute mobile bookers.