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.
A helpful site with tips on using both services is . . .