The movies I'd wished I'd seen in the theater are numerous and I could probably list fifty here right off the top of my head that I'm dying to see on the big screen. I've been fortunate to catch quite a few in the revival theaters over time, though there's plenty I still want to see. Of those, I'm going to go with these two, as I think they're both particularly crying out for a big screen viewing.
Before 1970: Where Eagles Dare (1968). One of my favorite war movies, one the family watched all the time growing up, the story that introduced me to Alistair MacLean, and that introduction, changed my life. This movie has sweeping on-location scenery, and that wonderful nasty cable car journey and fight that I would just love to see in a darkened theater. I'd love to see Richard Burton and Clint Eastwood wreaking havoc big screen. This is a movie meant for the big screen, and if it ever gets shown somewhere, I'll do my darnedest to try and get there for the viewing. (Really, I'd like a triple feature... this one, The Great Escape, and Von Ryan's Express -- three of my favorite war films that all require the big screen for proper viewing.)
Post 1970: Galaxy Quest (1999). Don't ask me how I managed to miss this one, but I didn't discover this one until later, on DVD. The rest of my family saw it in the theater, but for some reason, they just didn't make an impression on me that hey, you don't want to miss this one. It promptly became a family favorite when it was released on DVD and I kicked myself for missing it. I'd love to see it re-released.