Wow, hardly any mentions of "Star Trek: First Contact". Always disheartening and bewildering to see the lack of support and even hatred towards that movie here. To me, it's so clearly the best of all the movies with the acting, special effects, and writing all coming together perfectly and beautifully, while all the others have very frustrating flaws in one or more of each of those areas.
"Star Trek: The Wrath of Khan" is the only that I think is even close. I used to think it was better and I still think they're almost equal...it's just that "Star Trek: First Contact" outclasses it so dramatically in special effects (which isn't that important, though). Those two are just awesomely entertaining (and thoughtful, and moving) from start to finish whereas the others all have story problems and more (although the new one does come close to them in terms of pure entertainment for extended periods).