Happy Gilmore and Billy Madison are obviously his best movies. Punch-Drunk Love is also a very good movie. He was also pretty good on SNL, remember Lunchlady Land? He also had a couple solo comedy albums that were pretty good. I stopped watching his movies after Mr. Deeds. I don't really remember much about that movie, but I remember thinking it was just awful. And pretty much everything after that has disgusted me so much, just from the trailers, that I haven't bothered to see anything else. It happens a lot with comedians - they start out as a decent stand-up comedians, maybe get on a show like SNL or some other sketch comedy thing, then they make a few really good movies - and then at some point their movies turn shitty, and then they just continue making shitty movies until they die. Actors like Chris Farley made a good career choice by dying. If he were still alive, he'd probably be doing the same shit as Sandler.
Theres a video that breaks down his movies as excuses for advertising and payouts for his friends. Basically what they do is pay Sandler a large fee to do the film and every other scene has an advertisement for a product. The fees also go to Sandler's friends who appear in the films. you can see it here http://redlettermedia.com/half-in-the-bag-jack-and-jill/
The last good sandler movie I saw was little nicky, and it still sucked compared to his earlier work. Click was the point when he went from ok-comedian to completely unfunny and borderline stupid with a preachy backdrop to look more serious