The fourth film in the "Star Trek" franchise, released in 1986. Directed by Leonard Nimoy and written by Nimoy and Harve Bennett. It's one of the few Star Trek movies you can rent without looking like a rabid foaming Trekkie, because it's got a decent story and it's funny as hell.
When Earth is attacked by a deep-space probe, the crew of the Enterprise (currently aboard a Klingon warship) realize that the probe is trying to communicate with Earth whales. Unfortunately, whales have been extinct for several centuries, so the crew travels back in time to the late 20th century to catch some whales.
The movie has some great moments like Kirk and Spock (who's recovering from being dead) arguing about whether or not they like Italian food, Scotty trying to figure out a 20th century computer ("Helloooo, computer."), Chekov asking a police officer where the "nuclear wessles" are, and McCoy acting shocked over the primitive and barbaric medical conditions in a hospital, as well as funny lines like "I think he did a little too much LDS," "Everybody remember where we parked," and "Yeah? Double dumb-ass on you!"
I tend to despise Trek movies, but this one's good, like one of the episodes of the original series where everything'd get goofy. Where the hell's Harry Mudd anyway?