The original Star Wars for sure, followed by Empire Strikes Back. I have no idea how many times I've seen them; a few times a year for about 25 years, with some years having periods of watching them a few times a month. At least a hundred times, at least the original. Sometimes I can't actually believe I still enjoy it--I sit down and watch it each time and it's like the first time all over again, somehow it still entertains me. My family would always say that, they'd see me clicking through the TV stations and I'd find Star Wars on and I would just sit and watch it and they can only say "how many times have you seen this movie?" It's also the film I've seen the most in theatres, since I saw it five or six times in 1997 (otherwise Inception takes the cake at three or four screenings).
Other than that, the list of most-seen films for me is a bit random. I'd probably say these are contenders for the list:
-Terminator
-Predator
-Indiana Jones and the Temple of Doom
-Superman IV
-Matrix
-Jurassic Park
-Transformers: The Movie (1986)
-Aliens
-Alien
-Wizard of Oz
-Dawn of the Dead
-Ravenous
-Spaceballs
-Cocoon
-Neverending Story
-Evil Dead II
-Fight Club
A mix of a lot of stuff I watched a million times as a kid, and still do to this day, and stuff I discovered as a teen. I would say the Terminator possibly tops the non-SW list, as I had it on tape when I was five and loved it and didn't see Terminator 2 until many years later. There's a lot of stuff that I also watched a ton when I was younger but then haven't watched that much since, like Willow and Masters of the Universe. Goonies, Star Trek II and Who Framed Roger Rabbit are also runners up, but I feel like I don't watch them that much these days, maybe once every five years, while the rest I see at least every two. Actually I just saw Masters of the Universe yesterday (on Youtube no less) for the first time since the mid-1990s and it was much better than I was anticipating it to be, Dolph Lundgren and that pseudo-homo-erotic scene where skeletor has him whipped naked aside.
Actually, for someone who often has bad things to say about it, I've seen Phantom Menace almost as much as those. But hey, I guess it is in the same company as Superman IV and Masters of the Universe. I would probably remember TPM more fondly today if I just stopped watching it! Prequels: Good if you don't watch them. I also saw it four times in theatres, making it a runner-up for most-viewed theatrical.
Funnily, ROTJ doesn't even come close to making this list. I probably only saw it five or six times as a kid (haha, "only") and ended up tape-recording Super Dave Osbourne over parts of it. And this was way before the ROTJ Sucks meme was around! I know that I fast-forwarded to the space battle and lightsaber duels a bunch though. I had an idea when I was eight to make a dub which edited together the space battle into one long sequence, which I may finally do now! I tried to get this experience back then by just skipping from segment to segment; probably much easier now with DVD chapters. I guess the film always bored me except for a few action parts.