Incubus

Incubus started as a jam hard rock sort of band and as they became more popular gravitated toward a more pop rock sort of sound.  A good song to hear Incubus' jam sound is Idiot Box from an earlier album Science.  http://m.youtube.com/watch?v=lZmt5pJegcU As Incubus progressed releasing Make Yourself and A Crow Left of the Murder Make Yourself showed us some of the pop rock examples with Pardon Me and Wish you Were Here. A Crow Left of the Murder went back to Incubus' jam style in this song Angoraphobia.  Here you'll notice no scratching discs and a different guitar sound.  A change of bassist came with this album as well giving it a different approach.  More backup vocals in this song than previous Incubus tracks.  http://m.youtube.com/watch?v=LgaG1x--Ua0

Tool time

The band Tool has made many changes throughout their career.  The first example here is from their first  album Opiate.  Sweat has a much rawer guitar and laid back bass and drum parts than the next examples.  youtube.com/watch?v=9izLcXH0Hu8. After three more albums a bassist change Tool released their latest album 10000 Days.  This album overall showed a huge change for Tool switching to a progressive rock style from their earlier hard rock metal style.  The song Jambi shows how during this album they used rhythm to drive many songs.  Another interesting thing in Jambi is the talk box solo near the later half of the song.http://m.youtube.com/watch?v=Noz6-KaT4fA

The Used

Similar to Avenged Sevenfold The Used started as a pretty standard sounding band in the "screamo" genre with one of their first popular songs A Box Full of Sharp Objects.  This song has the screaming heavy distorted guitar and effect drivin arpegiated melodies that became recognized for this genre. http://m.youtube.com/watch?v=Rhww-odwLLM.  Compared to that song The Bird and the Worm has  a feel that honestly gave me the picture of Coheed and Cambria mixed with 80's metal.  The classical slowed down texture of this song seats you in a very different place than A Box of Sharp Objects.http://m.youtube.com/watch?v=Zv9zDC5HaKs

Avenged Sevenfold

The nu metal band Avenged Sevenfold from Hunington beach California started out living up to the nu metal sub genre with their quick guitar riffs and heavy rhythm breakdowns.  The song that gives a good example of this is Unholy Confessions from Waking the Falling.  http://m.youtube.com/watch?v=I-QaFWURsMU.  Next the song Seize the Day from almost five years later.  In this song we aren't hearing the chugging guitar and quick scale runs, here we have gone to a pretty standard pop rock sound.  http://m.youtube.com/watch?v=wheJrsRiuCM. I feel with this kind of change you are taking a big risk of loosing your fan base.

Stone Temple Pilots

http://www.youtube.com/watch?v=x2_dGkqYu6MThe Stone Temple Pilots changed in their career in these examples, the first being Plush from their first album Core.  This song has a much more typical rock style compared to the second example Art Song Girl that mixes a sort of twangy guitar sound with ridiculously distored guitar and repeated lyrics. 
This change in style wasn't as immediate as some other bands I've noticed changing.  Stone Temple Pilots stuck to rock style in their second album Purple with only a hint of diverting to the sound that Art Song Girl has.
http://www.youtube.com/watch?v=IbXlJDxVQZg

Comments are appreciated! 

System of a Down changing systems

http://www.youtube.com/watch?v=DX2RWSzBKio http://www.youtube.com/watch?v=5oLfM30A7Ko
http://www.youtube.com/watch?v=5oLfM30A7Ko

System of a Down is a artistic group that almost always has changed voices throughout their career.  By this I mean having the two different writers in the group that turned out some pretty different styles from time to time.  The first example I'd like to play for you is from System of a Down's first album titled Sugar.  Here System plays a pretty straight forward metal song.  The next comparison is She's like Herion from a much later album Hypnotize that brings a odd sorta metal sorta industrial sound forward with Serge and Daron doing harmonies almost the entire album unlike previous sing scream sing scream.