Say you want to go to the India/Thailand/China area and you are very flexible in terms of dates and also in terms of which country you fly to but are on a low budget, what is the easiest website for finding the cheapest flights?

All websites I have found expect you to have an exact day of outward and return flight as if we are all totally inflexible in that regard. I'd prefer a site that shows flights for a multitude of dates so you can select the cheapest.

Failing that, or rather an additional consideration is what flight checker is best for finding the very cheapest flights?

Thanks for your suggestions, time saved on many peeps part I hope.