SkyScanner is frequently recommended here on AB. It's good for bargain flights but, in some circumstances, it's still better to try individual airlines.
http://www.skyscanner.net/
There are people here on AB who can come up with some good suggestions. Just tell us where and when you want to travel. Don't forget to indicate whether there's any flexibility on dates (it's nearly always cheaper to travel mid-week) or destinations. (Sometimes flights can be very expensive to one airport while a resort just along the coast is served by some really cheap flights). Also, if you're going to ask for help in searching for flights, please remember the one bit of information which nearly everyone forgets to provide - wherabouts in the UK you're starting from! (There's not much point someone recommending a flight from Southampton if you live in Glasgow!).
Chris