Check the mileage run forum here, lots of stuff announced over there.
Sign up for all the special e-mails at every airline that flies anywhere near where you live
Check the dream maps over at travelocity
Use the deal detector over at Orbitz
Set the Fare Watcher over at Travelocity
Check the SAS website on the 12th and 13th, if last year repeats itself some incredible sales will be announced one of those days, one day only.
All that being said, not every route is on sale, and some places, like Europe in the summer, mignt not ever be an incredible sale. I bet April will have some incredible trips though.