Cheapest possible flight, don't care when!

[militantmandy]

Basically,I'd like to fly to Thessaloniki in Greece, from Edinburugh (or Glasgow if necessary). I don't care when, I just want the cheapest possible flights. Does anyone know of a site that will allow me to search within a tmeframe (ie 2010-2011), rather than specific dates? I can pretty much take my leave whenever I want, but there seems to be huge variation in flight costs.

Any help muchly appreciated!