Try airport websites directly.
Punch into their arrivals/departures board.
See who's coming in and taking off, then check the airlines websites for prices.
There are some great last minute deals to be had.
Never be afraid to tell an airline that you want to fly tomorrow and see what they say. It won't work with budget carriers, but for the likes of Qantas, Delta, BA, KLM etc., occasionally they'll offer you a good deal just to get the seat occupied. Also, sign up to their late deals email alerts. They'll contact you if there's a special offer on the destinations you've asked about (it's always best to say 'All' destinations though).
You don't of course have to be travelling tomorrow at all, but it'll give you some indication as what's on offer.