In any episode of the French cartoon Dragon Hunters and especially in its full-length 3d-prequel you may enjoy this trope with full conscience.
The Fleischer brothers were absolute masters at this. They had little 3D model sets that fit perfectly into their cartoons, and sometimes they seamlessly matched them up with their hand-painted backgrounds (i.e. during a cut in "Protek the Weakerist"). This was long before computers, mind. See Popeye the Sailor Meets Sindbad the Sailor for example.
Terrytoons, surprisingly for a studio of it's unfortunate reputation, have some of the most beautiful background art of all the Golden Age cartoons, with gorgeous composition, and beautiful rendering and color styling. Even their B&W films have slick, attractive looking backdrops, but the stunning backgrounds really become obvious once the studio started making color cartoons ("String Bean Jack", their first color cartoon in 1938, perfectly demonstrates this, with very atmospheric, rich backdrops, and amazing perspective work).
Batman: Gotham Knight did this with the first of its six shorts — the backgrounds are very beautiful and detailed, in contrast to the character designs, which are very simple and jagged.
The animation of Star Wars: The Clone Wars is very beautiful with very expressive faces, smooth movements, visually appealing character designs, beautiful art style, and downright gorgeous action sequences. The animation quality of the Pilot Movie and first season was debatable (especially with the early production episodes), but it was still decent for an all-CGI program. As The Clone Wars progressed, the animation quality improved and the characters moved more naturally. Even in the early episodes, the action scenes were impressive and the environments very detailed (including some extras most wouldn't notice on the first watchthrough of an episode), and by the second season and onwards, the animation quality and of detail were very visually appealing and near-cinematic.
In just the second episode of Futurama, they managed to do this with the Moon.
Code Lyoko should be the posterchild for this trope. The lead background painter by the name of Frédéric Perrin created meticulous backgrounds which were utilised in almost every scene in the non-3D sequences of the show; Indoor, Outdoor, Industrial, Urban, Nature, you name it. Check out his work for yourself.
The animated series Dungeons & Dragons features quite a bit of Scenery Porn, especially when showing what formidable landscape the teens had wandered into that week.
Hanna-Barbera might've had low budgets for their cartoons but many of their late fifties early sixties cartoons have beautifully painted backgrounds. John Kricfalusi talks about the paintings here.
The cartoon To Spring, which also has lots of Technicolor Porn with all the garish paints.
The Simpsons: "The City of New York vs. Homer Simpson" has a few examples of this, including the obligatory leaving-Manhattan-via-a-bridge ending (and "camera" zoom out).
The Teenage Mutant Ninja Turtles (2003) episode "The Ancient One" is full of these, once Leo arrives at the hidden land, where the backgrounds, instead of being in the series' usual style, are painted in a manner reminiscent of Avatar: The Last Airbender.
While not exactly unimaginably detailed, the backgrounds from the Looney Tunes Wile E. Coyote and Roadrunner shorts were◊ very◊, very◊ pretty◊ and had gorgeous colors.
The House of Mouse Prop Room (an extremely large basement that's supposed to house different props and backdrops for (almost) every animated Disney movie ever made), which for some reason, looks like something drawn by Mike Mignola of all people! Guess which Disney movie Mignola was involved in!
The French animated series Wakfu takes a few cues from anime... including gorgeous artwork. While this devArt page offers more characters than background, those backgrounds you do see with the characters are the barest sample.
Of all shows, Family Guy can do this when they want to. It's usually when they're trying to make the setting romantic or just pretty, for whatever reason. A more specific example would be the walk on the beach Adam West had with Lois' sister.
Thundercats 2011, is flush with many exquisitely rendered, unique environments jam-packed into each episode, detailed (and spoiled) here.
My Little Pony: Friendship Is Magic manages to pull this off in its Sugar Bowl of a Flash cartoon (take this shot◊ for example). The color, fluidity and amount of tiny details crammed into general shots are impressive. Some episodes use backgrounds that have never been seen before and are unlikely ever to be seen again, like the Training Montage in "Call of the Cutie", the fall foliage in "Fall Weather Friends", and the Wild West scenery throughout "Over a Barrel". There's also the pegasus city of Cloudsdale, an entirecity made of clouds and rainbows. Its a pretty Sugar Bowl! In fact, Cloudsdale◊ looks very similar to Mount Olympus◊ from Disney's Hercules (which also falls under this trope).
Motorcity manages to make a desolate, run-down, subterranean Detroit look absolutely gorgeous.
Coupled with a kickass Instrumental Theme Tune, Gravity Falls has one of the most beautiful animated intro themes for any cartoon show in recent memory, especially considering that it's from the Disney Channel. Even the animation within each episode conveys the show's setting in the Oregon countryside to a tee.
Steven Universe has pretty impressive background art as well, as seen here. Just look at Pearl's Room or the Communication Hub.
The animated If You Give a Mouse a Cookie series looks like a picture book brought to life and in particular has some very gorgeous backgrounds, like of sunsets or the starry night sky. There's also plenty of colorful detail to be observed on things such as tents and flowers.
Tumble Leaf has a gorgeous setting, in a forest with mossy stumps, fountains, colorful fuzzy flowers, and a wrecked ship on the beach that protagonist Fig the Fox lives in.
Hilda, as the series usually have transitions, which are magnificent scenes of the wilderness filled with monsters and creatures, or the city that feels alive with humans live in it.