Casual Time Travel

""Crossing into established time streams is strictly forbidden. Except for cheap tricks.""

- The Doctor, "Smith and Jones"

A setting where time travelling is common place. Having a time machine is nothing special. These are no longer "prototypes" or dangerous, unique devices made by a handful of Mad Scientists. No, they are common items, mass produced (though perhaps of restricted availability). It is like owning a car, or, at most, like taking a vacation. Time travel has long been mastered and integrated in society, and no doubt there are businesses specialized in Time Travel for Fun and Profit. There might be a Time Police enforcing the rules - in fact, Time Police almost always come from a setting with this trope.

Anime and Manga

 * The future humans of Haruhi Suzumiya are like this, as part of The Singularity.
 * In the 22nd century, apparently everyone can afford a Time Machine. Time travel becomes extremely common place. As a result, many lunatics have the idea of using future tech to exploit and alter the past, which calls for the existence of Time Police.

Literature

 * The Hitchhiker's Guide to the Galaxy does this a bunch (only when it would be funny, of course) but the Restaurant at the End of the Universe stands out; it's easy enough to get to the temporal end of the universe that it's a tourist attraction.
 * "Such Interesting Neighbors" by Jack Finney is a short story where time travel is so casually available, in a future that's such a Crapsack World, that literally everyone in the world goes back to live in their favorite time in the past.
 * Semi-example in A Sound of Thunder. They're not mass-produced, but a company offers vacations to the past.
 * "Needle in a Timestack" deconstructs how bad this can get in a setting that doesn't have Time Police—one narcissist with relationship issues manages to destroy a lot of lives.

Live-Action TV

 * Doctor Who Time Lords practically all have - or had - TARDISes, although only a handful ever got involved in the universe at large. They even set up their society as a form of Time Police. Many, many advanced other species are known to have a very casual relationship with their mastery of time travel via various technologies. Humans have developed at least two groups with time travel- The Time-Agents, (Once including Capt. Jack Harkness) and those who run the Teselecta, robots which go and extract unpunished war criminals like Hitler from the time-stream to punish them, and Daleks have time-travel technology as well.
 * Star Trek has this. Pretty much every warp-capable starship is capable of time travel with little not no effort - the plot of two movies revolve around ships going back in time with little to no preparation before hand. Though in the case of First Contact, the enterprise was following another ship designed to time travel, but seeing as they got back to the future on their own, the Enterprise-E is fully capable of this. Starfleet even has it's own Time Police to monitor time travel incident.
 * Star Trek is complicated. Logically, it OUGHT to be this trope. However, they seem to "discover" their time travel capability each time, so it's more of a illogically recurring New Powers as the Plot Demands. Episodes taking place in the future (of the series) are exception to this, they have casual time travel. The expanded universe usually handwaves it as parts of the Federation knowing about time travel, but it being really, really, really classified, so it never spreads.
 * In the alternate future in the series finale of Voyager, a Klingon scientist had developed a device which can send you anywhere and anywhen instantly, and while this future eventually never happened, the fact that it showed up at all and there's no obvious reason why the guys development would be stopped means that its quite possible that in the future the Klingons get involved in this kinda stuff. It's not like they'd be able to police it the same way the federation does.
 * Phil of the Future is about a family from the future where time travel is commonly used for vacations getting stranded in the present when the time machine breaks.
 * Goodnight Sweetheart qualifies - Gary Sparrow's time travelling is accepted as normal by his friend Ron.

Video Games

 * The Fongoids were like this in the backstory of Ratchet and Clank Future. The Zoni took pity on the Fongoids and gave them the secret of time travel to make their lives easier, and the resulting paradoxes led to both the construction of the Great Clock and the Fongoids swearing off time travel for good.
 * In The Sims 3 with the ambitions addon you can build an time machine as inventor and sell it on the commision market for everyday use.

Web Comics
" "In the McNinjaverse, time travellers are more common than the winning McDonald's Monopoly properties." "
 * In Bob and George the characters use time travel a lot—even though they hate it.
 * There's a Subnormality strip set in ancient Egypt where a woman expounds on all the glories of the Egyptean Empire, and how much they've developed both socially and technologically in the past decade. She then speculates about how the far future will be even MORE glorious... at which point her boyfriend accidentally lets slip that the future is such a Crapsack World that ancient Egypt looks a lot better, causing people to flee the present for the past. Quite similar to Such Interesting Neighbors, really.
 * And then this shows up as a new time traveller randomly appears in one panel, only to be killed in the next:

Western Animation

 * The Family Guy film shows this happening in 30 years. With time travel becoming the new form of tourism, and affordable too.
 * Not time travel per se, but in the "Go, God, Go" episode of South Park, a special devise allows people in the 25th Century to talk to people in the past. It is sold to children and used mostly for prank calls.
 * They actually forbid people from using the time phone to change the past. Good luck enforcing that.
 * Eric Cartman would grow up to make a fortune starting the first company specialized in time travel but his present self's reaction to being told this ruined everything.
 * The very premise of Time Squad is this, a time police assigned to prevent important historical figures from unintentionally rewriting history for the worse. They are so good at it, by the year 1 million AD, bacon is good for your heart.