Many think wrongly that contacting a hotels or airline directly leads to the lowest price for a room or airline ticket. This is often NOT true, though you should generally view the hotel or airline's own website for the rate because an increasing number of hotels are offering price guarantees if you book via their sites. Note that generally this creates a large savings for them because they don't have to pay a commission. Unfortunately booking via the hotel sites rarely saves you more than a few dollars of savings vs the lowest online rates.
There is NO magic bullet or specific website or simple technique for finding cheap rates, rather you need to to surf around and look for "consolidators" that are *usually* cheaper than the hotels or airlines themselves.
Hotels.com is a large and popular consolidator, but Travelocity, Expedia, and Priceline are also major consolidators and there are hundreds of smaller ones. In Europe, for example, any of those or Venere - a consolidator focused on European hotels - may find you a cheap room.
I have NOT used Priceline much recently because in the early days it was frustrating to work with and I found few rates that beat Hotels.com. My belief now is that Priceline is generally only a good choice for higher end hotels and then only if you have the time to search and wait for good rates and the flexibility to change hotels and plans as needed to get a good rate.
Kayak.com is an excellent service that allows you to search different airports and airlines quickly and easily. For example in June of 2006 I found Kayak's American Airlines rate was lower than the airline and lower than all other consolidators. I'd guess Kayak had a special deal with American for this route.
An example of the consolidator advantage: In early 2006 I used a small flight consolidator called cheapseats.com to book Delta to Boston and paid about $100 less than the cheapest fare Delta had online at the same time. This situation is common in travel because pricing is very market driven and surprisingly inconsistent both for flights and hotels.
As a travel publishing guy I know how some of the hotel deals are cut and it's a very sloppy and counter-intuitive process where some consolidators will force properties to sell them blocks of rooms far below rack rate in exchange for a guarantee of selling those rooms. Hotels.com is notoriously unpopular with many hotels as the top consolidator because they tend to squeeze great deals from properties in exchange for guaranteed volume and lots of bookings. Good for you the consumer but hard on the profit margin for the properties.
If, at the last minute, the consolidator has a lot of rooms left they may sell them at rates far below what the hotel will charge if you call them. You especially see this in places like Vegas and big cities. During a November Vegas trip I got the Hilton through (Travelocity I think) for about $55 which I think was under their own website rate and under the rate at other places I checked. Yet during a March trip I found the best price for Oriental Palace at their own site - an excellent $65 nightly for a nice room in the middle of the strip plus some buffets. (though I did have to switch rooms due to noise from a room in the wing above Harrah's, which features an outdoor rock music pavillion open until about 2pm).
