Online flight search facilities

Each of these services search several or all of the airlines for the best fares:

www.kiwi.com
www.orbitz.com
www.travelocity.com
www.kayak.co.uk
www.cheapflights.co.uk
www.ebookers.com
www.expedia.co.uk
www.netflights.com
www.opodo.co.uk
www.skyscanner.net