Looking for discount last minute flight site

[SpiderMan]

Someone told me a while back about a service that would give you really last minute flights at very very low prices but you couldn't really pick when or where. I'm just trying to get to Europe sometime soon but pretty much every aspect of my trip is flexible. Departure date, return date, destination city, even departure city as long as I have enough notice to get a bus ticket or something. Does anyone know of a website like this? Supposedly this site would tell you that there was a flight to Warsaw (or whatever) in 2 days for $XXX or something like that.

Thank you so much in advance.