The Audi TT 1.8T engine should go straight in..........I think you'll find its a popular engine upgrade. Someone posted a while back a list of engine options for different Mk's, I'll see if I can find it again.
Are you looking to fit it yourself? You'll need the ECU and probably some other bits and pieces as well as the engine itself. If you're getting everything you need to do the conversion for ?2K, then that doesn't sound too bad to me.