Current favorite Italian phrases/words:

Ma non e` vero! (It's not true!)
Dondolare (the way that young people dance in clubs, bouncing around)
Ho da fare. (I've got some stuff to do.)
L'hai fatto apposto! (You did it on purpose!)
Dammi cinque! (High five!)
Noi siamo gran mangiatori di biscotti. (We're great cookie-eaters.)

I learn a lot of new words, but then I forget them. Usually it takes a lot of repetition to remember it, but listening to my Italian family speak helps a lot.