Priceline and Hotwire
I don't use Priceline or Hotwire for air travel (except in rare occasions) and I haven't found their rental car deals to be that great, but you can really get some great deals on hotels. I just stayed at the 4-star Hyatt in Austin overlooking the waterway for just $50 per night (plus fees and taxes) by using Priceline. And, I have booked some good hotel/car deals at Hotwire from time to time.
I can't go into an exhaustive explanation on how to use these sites, but if you are interested in saving serious money on travel, check out Priceline and Hotwire.
A helpful site with tips on using both services is . . .
BetterBidding. This site provides helpful tips on bidding on Priceline and Hotwire and ways to make sure you get the hotel you want. Another one you can check is Bidding for Travel.
I've found some of the best rental car deals on Orbitz, which gives you a comparison among 6-8 rental car companies.
For the best airfares, I usually check out Orbitz and OneTravel along with the airlines home sites. And don't forget Southwest. I flew round trip TUL-STL for a $68 fare a couple of weeks ago.