… and continue to be successful with that new style?
I asked myself this question after listening to a fairly recent Mariah Carrey song. When she burst through the scene she was doing a lot of ballads, some romantic songs, Jackson 5 covers, that type of thing.
I really liked her music back then.
Her new stuff is mostly meh. Her vocal skills are undoubtedly still amazing but the R&B/Hip-hop style is not my favourite nowadays.
Anybody else?
Pantera went from really over-the-top glam rock to Cookie-Monster-type groove metal.
Ministry went from straight early-'80s bubble gum pop to grinding industrial metal.
It really is night and day with both of them. Metal Magic is a long way away from Far Beyond Driven, and With Sympathy is barely worth mentioning compared to Psalm 69.
Linda Ronstadt. From folk to rock to Broadway to Standards to Mexican Folk to adult contemporary.
They continued to transition on the last two albums. They now sound more straight ahead metal, very little industrial sound.
Also, Tom Waits went from lounge style crooning to…to…well, I don’t know how you categorize his newer stuff. He changes his style every album now.
The BeeGees went straight from 60s pop to 70s disco without missing a beat.
Bob Dylan. His change from traditional folk musician to electrified folk rocker, at a minimum.
Beethoven.
Thomas Dolby wrote synthpop in the earliest part of his career. (The Golden Age of Wireless, The Flat Earth), although he did play keyboards on Def Leppard’s Pyromania album in '83 (credited under the pseudonym “Booker T. Boffin”). He then mellowed out with more stylish pop songs around 1986 (Aliens Ate My Buick). After that he experimented with jazz and soft rock, which he still writes.
Howard Jones is a similar story, writing synthpop/new wave, then straight pop, but after '86 or so, he experimented a lot with ethnic sounds for years. Only on his most recent album a couple of years ago did he switch back pop.
Depeche Mode were a synthpop act throughout the 80s, but in the 90s started introducing a lot more guitar and a more rock sound to their act; with the album Ultra and the first single I Feel You they let rip with electric guitars and a bit of an epic sound. Except for one or two songs, each album since has been either soft rock, or something with a lot of guitar work.
Herbie Hancock was always associated with jazz in some fashion, but in the earlier 80s he entered new wave and contemporary dance music with the seminal classic Rockit. While Rockit was a commercial success, the album Future Shock didn’t do well, nor did the two followup albums in a similar vein – in fact, they are considered the worst of his career, so he returned to his jazz roots, though more modern in style in the form of acid jazz.
Ministry was already mentioned, but Al Jorgensen made the switch because his first releases were under his record company’s direction and he hated them. Once he was able to take his own direction he went with what he was more comfortable with: Metal.
If you mean the switch from the Middle to Late, then he wasn’t really successful with the late works e.g. the quartets, within his lifetime (the Ninth’s an one-off). They became popular a few decades hence. Although the change pre & post Heiligenstadt may qualify, if you count him as a successful composer (not performer) at that point.
Jeff Beck
I’m not sure if you count an artist’s style change after leaving a from a former band, but…
Darius Rucker, while fronting Hootie and the Blowfish, was solidly rock/alternative, with Cracked Rear View being a huge album.
He is now a country singer with several number one songs. He even won the CMA’s “New Artist of the Year” for 2009.
The Beatles. More accurately, they tried many different styles and were successful in nearly all of them.
Maybe panache means that he went from composing to decomposing. 
Thank you.
Sting went from self-absorbed, world-music influenced neo-reggae pop with the Police to self-absorbed, smooth-jazz influenced neo-crooner pop with his solo career…does that count?
Prince went from straight up R&B on his first two albums to radically different synth pop with Dirty Mind…
Gotta run
Rush went from sounding like Led Zeppelin interpreting Ayn Rand to The Police interpreting Ayn Rand.
Does, say, the Greatful Dead going from amped-up psychedelic to acoustic neo-bluegrass/proto-alt-country count? (If you include them doing occasional songs with the Beach Boys, does that count?) After them, it’s kind of what almost every psychedelic band does, but there’s pretty distinct styles there.
I’d say Radiohead has changed over the years.
1993:
2000:
2008:
Pink debuted as an R&B-esque singer with “Most Girls” and now is more of a Lita Ford-esque rock chick. I think most singers change once they become successful because their first album is inevitably under the thumb of the record companies. After they prove themselves a hot commodity, they are allowed to experiemnt with other styles a bit more.
My favorite band, Queen, would drastically change styles in the same album. And it worked, because they were all so freakin’ talented at anything they did, from hard rock to gospel.
The Killers first album “Hot Fuss”, when they were all dressed in black and wearing eyeliner and looking all emo, I would take on a deserted island with me.
Their second album, when they changed their style of music and dress and became all wild-west looking, imho, sucked.
Their third album, which seemed to be a little dancier, imho, sucked.
(But when I saw them in concert this past September they were awesome. :))
Or you go the opposite route – indie type sensations to bland pop sell-out. I immediately thought of Liz Phair here but it applies to any number of musicians who hit success.
I’m speaking of perception here rather than trying to debate whether Ms. Phair (or anyone else) actually “sold out”.