How to find cheap flights when dates aren't important?

rodhull

OK, so I've used a number of websites to help find cheap flights when I know the dates I want to travel (see Martin's cheap flights article), BUT, what's the best way to find the cheapest flights when dates aren't important?

For example, I'd quite like to travel somewhere in Central America (Mexico say) for 3 weeks at some point between early February and late May. I don't mind too much when exactly, but just want to find the cheapest flights.

Are there any websites where you can enter origin and destination airports and a trip duration, that will then find the cheapest time to fly, or do you just have to try every combination? Even better, can any website do the same but suggest a different trip length in order to save more?

If not, why not!?

richardw

FYI

http://www.mexicana.com/cs/Satellite?blobcol=urldata&blobheader=image%2Fgif&blobkey=id&blobtable=MungoBlobs&blobwhere=1225910527553&ssbinary=true

hollydays

but dont forget to check the weather at the cheapest times