When one thinks of a time travel story, one usually assumes that some form of vehicle is used to transport the protagonists to and fro in time. While the early examples of time travel usually involved a knock on the head or some other sort of loss of consciousness, modern stories are more reliant on devices.
Such devices can be small and portable, like a watch, or large and stationary, such as Mr. Peabody's WABAC machine. They can even be huge, like a space ship, or even alive, like the telekinetic dragons of Pern.
Sometimes, the vehicle itself isn't a time machine, but it permits access to a means of travelling in time, such as the Road in Roger Zelazny's novel Roadmarks.
Among the zanier time travel devices are a malfunctioning toaster (The Simpsons), a cardboard box (Calvin & Hobbes,) a stolen map (Time Bandits,) a hot tub (Hot Tub Time Machine,) and a peculiar hat (the Twilight Zone episode "Once Upon A Time.")
Of course, most time travel devices are actual machines, of one sort or another, and the more flashing lights and moving parts, the better. George Pal's vision of H. G. Wells' brass-and-ivory time machine is iconic, as are the DeLorean and the 1897 model Rogers 4-6-0 steam engine from Back to the Future, as well as the blue police call box TARDIS from Doctor Who. In homage to the TARDIS, Theodore Logan and Bill S. Preston, Esquire, travel around in a telephone booth given to them by Rufus, a man from the future, in Bill and Ted's Excellent Adventure.
Starships often serve as time machines. The USS Enterprise travelled through time on several occasions, and the Heart of Gold used the Infinite Improbability Drive to simultaneously pass through all points of the universe, which included stopping for dinner at Milliways, the Restaurant at the End of the Universe.
As evidence of their importance to modern life, computers are often involved in time travel, taking the place of magic in opening up temporal rifts or wormholes through which people can access history, or creating extremely realistic simulations of other times and places. Mr. Peabody's WABAC has already been mentioned, and I gave a review of The Great Time Machine Hoax several weeks ago. The Time Tunnel involved a huge and tremendously expensive government project, in which two men were able to physically travel through a corridor into different time periods, often changing history. The similar series Quantum Leap had the main character's personality projected into the lives and bodies of people in order to effect history.
Another government experiment uses a maser which accidentally sends a passing motorcyclist back to November 5, 1875, where he (and his ride) attracts the attention of a band of desperadoes, and becomes his own great-grandfather, in Michael Nesmith's Timerider. Curiously, the date of November 5 also appears in Back to the Future.
While some time travellers inadvertently alter the future by their actions in the past, other travellers use time devices in order to make sure the present turns out the way it's "meant" to be.
The Voyagers in the TV series of the same name used exquisitely designed Omni-Chronometers, or Omnis, to keep tabs on history. And of course, time devices can be used to alter the past in order to change the outcome an action has on the present, such as when Hermione Granger used the Time Turner pendant given to her by Professor McGonagall to save Sirius Black and Buckbeak the Hippogriff in The Prisoner of Azkaban, or when Jason Nesmith uses the Omega 13 device to jump back in time 13 seconds and save his crew in GalaxyQuest.
Whether the product of a mad scientist, secret government program, or an alien technology, time machines will continue to capture the public imagination, as long as people wish to be able to change the past, or to see into the future.
Or just to be able to place bets on the next thirty World Series.