Which Airlines?

I am always on the lookout for useful resources for holidays and airline travel and one of the things I have felt the need for, is a site that can tell you which airlines are likely to run flights between your preferred start and end points of your trip.
Once you have decided which airports you can fly from, and which your preferred destinations are, you still need to find the airline before you can start comparing prices. If you find an airline that runs your chosen route, how do you find out if there is a cheaper alternative or one offering a better service?
This handy web-page should identify the airlines that run your specific route on the date that you want to fly. The only downside is that you must choose a day, if you are flexible about your flight days, you will have to do several searches to ensure that there are not other airlines running the same route on different days.