Hipmunk is a travel search site enables you to search for scheduled and low cost airlines in the one search. There are other fare finders that do the same, but Hipmunk present their results in a visual “timeline” that allows you to select the best flight at a glance. You can search according to price, flight duration, departure or arrival time, and unique to Hipmunk is the Agony scale, which combines the price, duration, and number of stops.
My favourite feature of Hipmunk is being able to conduct multiple searches without losing your previous search. To start a new search just click a new tab and a new search page will begin on a new page like a spreadsheet. You can then flick between pages as required.