Favourite is The Breakfast Club. It's really the best in terms of substance.
But I also love Sixteen Candles, Weird Science, Uncle Buck, and stuff he's written like Vacation and Home Alone.
Oh, and the best of the pure comedies.. Planes, Trains & Automobiles of course. A classic.
I love Home Alone, the bit where hes arguing with a french man in the hotel on the phone and says 'parlez vous anglais?' cos he clearly isnt getting anywhere!