These are obviously for when they are older, and I'm not sure if they are the type of movie you want them watching even then, but movies like Porky's and Hardbodies are pretty classic and aren't really done properly anymore. There isn't much in the way of anything redeeming in them, besides boobs, but still.
It's weird you brought up Porky's, because it's not really a good movie, but I remember it fondly. That, Meatballs, and Stripes. I think those were some of the first boobs I saw.
The other day someone asked me what my top 5 movies were, and I basically went with ones that I could watch every single month and never get tired of (you have some of these already):
Back to the Future
Back to the Future 2
Groundhog Day
Dazed and Confused
Shawshank Redemption
Other notables are Christmas Vacation, Big Lebowski, Good Will Hunting and Home Alone. Never get tired of them.
There are lots of other "best movies ever" like Godfather 1/2, Apocalypse Now, Seven Samurai, etc (basically anything on "top 100 movies" lists), but those to me are just too much to watch often.
Edit: Also throw in pretty much every John Hughes movie (even though above included some); Breakfast Club, Uncle Buck, Sixteen Candles, Mr. Mom, Dutch...fuck, they're all good. John Candy movies are also really good (especially when they overlap with John Hughes). Summer Rental is close to my "watch all the time" list. Fuck, and add Trading Places too. That should probably be in my top 5. It's right up there with BTTF and Groundhog Day.
Edit2: I was thinking about Trading Places and Jamie Lee Curtis boobs...and then True Lies came to mind. Damn that's a good 90's action flick. And then the list just keeps going from there. Total Recall, Terminator 1/2, Die Hard, Top Gun, My Girl, Blazing Saddles, Young Frankenstein, Spies Like Us. I feel like I could just go on and on clicking through IMDB.