I would like to say that the Map was one of the most useful items in the series, without it, so much would've been lost, but the thing that stands out in my mind right now is the moral support it gave to Harry in book 7, the fact that it enabled him to see Ginny when he needed it most really stands out to me.

So yes, thank you Fred and George for finding the Map, surely one of your greatest feats of trickery.