Click on the links below and see the sites that I usually use. Saving hundreds of hours of trolling through the internet:
Many of the sites that I have included in flights also offer accommodation, cars and cruises and vice versa in the accommodation section. However the way I've categorised them is how I've generally used them.
It's interesting to note that Priceline Group includes Booking.com, Agoda, Kayak, Rentalcars and OpenTable and Expedia Inc. includes Hotels.com, Travelocity, Trivago and Orbitz with CarRentals.com. Tied up in all these companies is CTrip (a Chinese based company that has invested heavily in online travel).
However the companies appear to operate independently and if you have an account with them you can often get a better deal than the "Group" price.