Another must have, it compares the prices of ALL the online companies like Expedia, Hotels.com, Priceline etc. I will give you a HUGE tip. If you are a points collector, you may be aware that hotels, for example, will not honor points if you don’t book directly with them. However, when you see a discount price on one of the outside services, always check the hotel’s website or call and you will see that the prices are often the same or a little more but you get the points. Kayak also can be programmed to send alerts to you about price changes.