I love Galaxy Quest. It touches all the notes of fan ardor, and the fact that the fans really do help save the world is so sweet. I also enjoy Tim Allen, who doesn't have huge range as an actor but is always warm and relaxed as Mr. Everyman. (I happen to like Harry Potter as well, though I understand that it's not everyone's cup of tea.)
As for Prince of Thieves not being a movie great, that's not necessary for one's favorites list. All you need for a movie that you watch again and again is for it to push your buttons in the right way. Maybe it's the one film that perks you up when you're down in the dumps, or you have special affection for the star, or it can relax you when you're tense. One of my favorite films is Music and Lyrics, with Hugh Grant and Drew Barrymore. There's something about the way they build the song they're composing throughout the movie that I find just enchanting, and then two or three of Grant's lines just make me smile every time I hear them. Nearby on my list of dependables is Doc Hollywood, with its town of eccentrics and Michael J. Fox as a fish out of water. And my favorite Hepburn-Tracy film isn't Woman of the Year or Pat and Mike, the two generally acknowledged gems of their pairing, but Desk Set, possibly because with its office setting it reminds me of my own life. None of these, except perhaps Desk Set, is an immortal example of filmmaking. But I'd rather watch any of them than Citizen Kane or Some Like It Hot or High Noon. I know you understand!
Bill Paxton (Twister, Titanic) is also in a starring role as Costner's rival. 
