There are many search engines available to assist one with securing flights. A few provide multiple price comparisons in one search. All are arranged alphabetically as follows:
MULTIPLE SEARCH VEHICLES
Bookingbuddy: http://www.bookingbuddy.com/flight.php Lists AirFast Tickets, CheapAir, Fareboom, FlightHub, Expedia, FlightNetwork.com, OneTravel, TripAdvisor & more.
CheapTickets: http://www.cheaptickets.com/cheap-flights/ Owned by Orbitz Worldwide. Lists CheapAir, Expedia, Hotwire, Orbitz, Travelocity& TripAdvisor
Dohop: http://www.dohop.com/ List several search engines.
Expedia: http://www.expedia.ca/Flights Lists CheapAir, Expedia, Hotwire, Orbitz, Travelocity& TripAdvisor
FareCompare: http://www.farecompare.com/when-to-fly/flight-search.html Lists AirFastTickets, Air Tickets Direct, Expedia FlightHub, FlightNetwork, & more carriers.
Hipmunk: http://www.hipmunk.com/flights-search Lists AirFast Tickets, CheapTickets, Expedia, FlightHub, Priceline & others.
Hotwire.com: http://www.hotwire.com/air/index.jsp Lists AirFast Tickets, CheapTickets, Expedia, FlightHub, Priceline & more.
KAYAK: http://www.ca.kayak.com/flights Lists CheapAir, Expedia, Travelocity & more.
Mobissimo.com: http://www.mobissimo.com/search_airfare.php Lists Booking.com, ebookers.com, Expedia, Orbitz, Priceline, Travelocity and more.
OneTime: http://www.onetime.com/flights Lists Expedia, FlightNetwork, OneTravel and more.
Skyauction.com: http://www.skyauction.com/air.do Lists AirFastTickets, Fareboom, FlightHub, OneTravel, Orbitz & more.
Skyscanner: http://www.skyscanner.ca/ Quite comprehensive! Lists most engines and more carriers. Budget travelers and flexible travelers will love this one. However great Kayak's search engine is, Skyscanner has the widest range of flexibility and options. Though Google's ITA software does the job, this engine shines by checking for fares on not just full-service carriers, but on budget airlines such as RyanAir, AirAsia and Tiger as well. It'll string together budget flights, making it the best place to go if you want some bang for your buck. Better yet, if you've got an open schedule, Skyscanner lets you search for flights in specific months or in years, or even just the cheapest destination from where you are. No destination in mind? This site is bound to give you some inspiration about where to go.
TravelGrove: http://www.travelgrove.com/ Lists Bookingbuddy, CheapAir, FlightNetwork, FlyFar, Priceline, TripAdvisor & more.
Travelocity: http://www.travelocity.com/Flights Lists CheapAir, Expedia, Hotwire, Orbitz, Priceline & more.
SINGLE SITE SEARCHES
Adioso: http://adioso.com/ Lists best, cheapest and fastest carriers.
Airfarewatchdog: http://www.airfarewatchdog.com/ (recommended for U.S. only) This isn't a search engine but a really great fare alert system. Once you sign up, the site will email you the cheapest deals (domestic or international, depending on your preferences) from your city base. It's a great way to keep tabs on a city that you eventually want to fly to. There's only one caveat, though. If you're based outside of the USA, it won't work as well.
Bing Travel: http://www.bing.com/ Bing Travel premiered to the public as Farecast on May 15, 2007.
CheapAir: http://www.cheapair.com/ Lists multiple carriers.
Fareboom.com: http://www.fareboom.com/ Good for international travel. List multiple carriers and cheaper dates.
Flightnetwork: http://www.flightnetwork.com/flights/ Based in Oakville, Ontario and founded in 1998, FlightNetwork® was re-launched in 2005.
FlyEurope: http://www.1800flyeurope.com/airfare.cfm Since 1995, offering travelers the service for air, car and hotel reservation services.
GetGoing: https://www.getgoing.com/ Allows one to submit two destinations to obtain the cheaper price.
Google Flight Finder: https://www.google.ca/flights/explore/#explore;f=YTZ,YYZ;t=r-U.S.,+United+States-0x54eab584e432360b%253A0x1c3bb99243deb742;li=3;lx=14;d=2014-04-25
Google ITA Software: http://matrix.itasoftware.com/#session=650e5916-f877-4cb9-8bcc-d0680485c326 This is the software that the search engines (Kayak, Orbitz and Bing) and the airlines (American, United and ANA) utilize. It will pull up every fare with full accuracy. It'll find complicated open-jaw itineraries and catch prices that even Kayak doesn't see. The only difference is that while it will tell you exactly how much an airline seat is going for, it won't tell you where to buy that fare. However, while trying the airline website first almost always works, Hipmunk can also replicate any itinerary you find. ITA should be your first search choice.
Opodo: http://www.opodo.com/flights Registered in Spain, Opodo is the first Pan-European travel service.
Priceline.com: http://www.priceline.com/flights/ Lists multiple carriers.
Routehappy: https://www.routehappy.com/ List multiple carriers.
Southwest Airlines: http://www.southwest.com/ Competitive prices from its own site.
TripAdvisor: http://www.tripadvisor.ca/CheapFlightsHome Lots of good reviews.
Zuji: http://www.zuji.com/ Operates in Asia Pacific countries.
Check the airline's own website to make sure the flight is not cheaper there, and don't forget that Southwest doesn't show up on most sites. It's often a good idea to book from the airline's site for to take care of the minutiae such as entering awards number, choosing seats, paying for extra luggage, as well as changing your reservation down the line if necessary.
Sites like Hipmunk drop flights with long layovers or sky-high prices down the list.
Priceline's opaque bidding system works well with hotels; you can save 30-50% on hotels by placing an absurdly low bid and allowing the site to charge your card before it tells you exactly which hotel you are paying for. Savings are less and rarer on flights, but do exist, particularly on domestic flights booked just a few days in advance. Savings top out at about 40 percent, so try bidding 10-20% below the cheapest standard fare. If your bid fails, no problem: Book through Priceline's regular service, which fares as well as other big-name sites on tests. Two caveats: You can choose the date but not the departure time of your flight (or the airline), and you might be stuck with an annoying layover. But other than advance planning, I don't know a better way to shave dollars off a standard domestic ticket.
When Your Dates or Destination Are Flexible
Most of the bigger sites (notable exception: Expedia) offer to find you cheaper flights if you're willing to fly one to three days earlier or later. Much better are the far more intuitive bar graphs you get on Momondo and Google Flight Explorer. There's also GetGoing, which will give you a discount if you give it two destinations you like and let it pick one.