Evan uses this website to locate the best fare for his flights - www.itasoftware.com

You can't purchase your tickets from this site and you do need to register (I think) before you can view flights. What Evan does is create a 30 day calendar around the dates he wants to travel and enter the origin and destination airports.. This site will bring up the lowest fares that meet his criteria. He then goes to the specific website to make a booking. I hope this isn't confusing!