cheap flights?

I have a friend coming over in dec. and am wondering what is a good site to locate and purchase a economical ticket .
departing Montreal going to Grand Rapids,michigan ..I have searched yahoo travel but I am sure there are other site availible – also are they safe to puchase online ?
thank you

Airfare Predictor:

http://www.farecast.com/

Airfare Alerter:

http://www.airfarewatchdog.com/

Booking Engines:

http://www.travelocity.com/

http://www.orbitz.com/

http://www.expedia.com/

http://www.hotwire.com/

http://www.priceline.com/

http://www.cheaptickets.com/

http://www.cheapflights.com/

http://www.faremax.com/

http://www.traveldiscounters.com/

http://www.lowestfare.com/

http://www.skyauction.com/

http://www.onetravel.com/

http://www.flights.com/

http://www.airlineticketsdirect.com/

http://www.cheapoair.com/

http://www.bookingbuddy.com/

http://www.travelzoo.com/

http://www.kayak.com/

http://www.travelation.com/

http://www.airfare.com/

http://www.airgorilla.com/

http://www.lastminutetravel.com/

http://www.ticketspinner.com/

http://www.lowfares.com/

http://www.travelgrove.com/

http://www.farefox.com/

http://www.economytravel.com/

http://www.bargaintravel.com/

http://www.travelcuts.com/

For Students & Faculty:

http://www.statravel.com/

http://www.studentuniverse.com/

List of Airline Websites:

http://www.geocities.com/Thavery2000/

How to travel cheap!