Vacation and Christmas Vacation should have been it.
Robocop needs no remake, those rat bastards...the movie is fabulous in it's own right.
Personally, I'd love to see Ghostbusters 3, but it'd HAVE to be Bill Murray, Dan Aakroyd, Harold Ramis and Ernie Hudson...last I heard, Murray was being a dick so fat chance of this ever happening.
Police Academy...eh that's a tough one...obviously Mission to Moscow should have never been made. I guess I'm in the Guttenburg camp, 5 and 6 would have been better with him in them. I've heard talks of remaking this as well.