For hotels, there is a group of us that have over reserved, so space is available to share or take off someone's hands.
For flights, I love kayak.com. It gives you great prices. Note that some airlines like southwest don't advertise on any of the discount sites though.
I'm also using Yapta- put in your route and it tracks when the price drops. Right now I'm expecting to pay about $200 RT for my airline ticket from Boston, so not bad.