Roger from American Dad is constantly dressing up, and wears outfits from various episodes during the opening sequence gag.
In MegaTokyo, most of the main characters change shirts every day or so. The majority of high school students are in uniform, though, so that’s not going to change much.
Cardcaptor Sakura had elaborate outfits for each episode’s card capture, clearly partly so you could tell they weren’t reusing footage.
The webcomic Questionable Content is pretty good about having the characters change clothes every day in the strip (some of which last for months of real time). They’re all twentysomething hipsters so the clothes tend to be different colored T-shirts, but they do change.
Grrl Power, a superhero webcomic, depicts the characters wearing different clothes daily. It’s not necessarily obvious, because most of the run has been a single (very eventful) day and many of the characters wear uniforms. However, in an early strip, we see the main character in 5 different shirts (in a set of one-panel flashbacks representing different days). The most recent couple of pages have shown her in another different shirt (a WW[Deadpool face]D? shirt that I now covet) and different shoes.
If we’re including comic strips, Frazz mostly wears a janitor’s coveralls, but he has a wide variety of t-shirts underneath (usually for either some band or some athletic event). Plus, of course, when we see him in biking or swimming garb.
There’s a local strip called Flo and Friends where the characters wear a variety of sweatshirts, mostly Cleveland-themed in some way.
No, I pretty much just meant any cartoon characters, whether from a comic strip, cartoon show, web series, or whatever iteration you can think of! 
Anybody mentioned Janet Van Dyne, The Wasp from Marvel’s Avengers, who never wears the same outfit twice? (Or, at very least, has more different outfits than any other comics character?)
Oh, another trivial example: Halloween issues! Mickey and Donald and Goofy all dress up like pirates and hoboes and Napoleon or whatever. (Clarabelle Cow looks really good as a witch!)
Avatar: The Last Airbender would update the character’s outfits periodically, as well as having one-off outfits related to the plot of the particular episode they’re in.
For a while in Chris Claremont’s run on X-Men, there was a running gag that young teen Kitty Pride couldn’t settle on a superhero costume, and was continually coming up with new ones that only a thirteen year old girl would wear. You can see some highlights (and… other… kinds of lights) on this humorous t-shirt design.
Wait, I’ve got the ultimate answer to the OP’s question: Garfield never wears the same clothes!
IIRC, the Archie comic books would have all of the main characters, and I daresay some of the minor characters, change outfits from story to story. I think this also happened in the TV animated series(eseses) as well, although probably not as frequently.
Disney’s The Weekenders cartoon from a few years back actually gave the cast multiple outfits, even changing them within individual episodes.
As a matter of fact, TV Tropes has a list of exceptions—scroll down to the bottom of the page. Anime and Western Animation would be the most relevant.
“Don’t come in! We’re getting dressed!”
“Uh, Rarity, we usually don’t wear clothes.”
All of the characters on Jem wore different clothes in every episode, usually with multiple wardrobe changes within each episode. (I realize this is reaching way back, but my 6 year old has just discovered Jem on Netflix…)
Elmer Fudd doesn’t wear the same clothes all the time. He has his hunting outfit, his formal attire, and his street clothes!
