Check out Farecast

There's a new kid in town when it comes to finding the lowest airfares. Called Farecast, it finds cheap fares between specific cities, but the really cool part is that it also can tell you whether you should buy now, or hold off a bit because the cost is likely to drop. It still just covers major airports, but likely will expand to the rest of the market as time goes on.

Thanks to Gary for the pointer!