Farecast uses airfare price predictions to help you figure out whether you should wait or buy your ticket now, depending on whether fares are likely to go up or down. Farecast told me the price for my ticket to Los Angeles was likely to go down within the next 7 days so I waited.
Meantime, I used Kayak to set a price alert so I'd know when the price went down. Kayak sends emails, and as soon as I saw the airfare had gone down, I bought it - and again, saved $100 on two tickets!
One more thing, HotelTonight.com allows you to book exclusive same-day hotel stays on your cell phone! Quick and convenient.