The Epic Saga of Decaydance (The Short, Short Version):
Once upon a time there was a boy named Pete Wentz, who played the bass and screamed in hardcore bands in Chicago, and he got bored with doing that and wanted to do something "just for fun." One day, his buddy Joe met a kid named Patrick in a bookstore because Patrick butted in on his conversation who played a billion instruments and sang like an angel. Later on they got a leftist vegan drummer named Andy, and Fall Out Boy was born. They ruled the Chicago pop-punk scene, and eventually got signed to a label called Fueled by Ramen, and later to Island Records.
Pete's got a... fondness, shall we say, for the internet. Like, it wouldn't be far off the mark to call him a BNF. So one day, a little kid from Vegas called Ryan Ross started talking smack about Fall Out Boy in Livejournal, saying that Pete should listen to their band, because they're awesome. So Pete (being Pete) did just that. And then he flew out to Vegas to meet them. Ryan and his little band called Panic! at the Disco played some stuff for him, and Pete asked him to sign to his record label. Then, he had to fly home and ask Fueled By Ramen if he could have a record label, and thus Decaydance was born.
A few artists from FBR have migrated to the vanity label, and Pete's signed about four or five more himself. They're a weird mishmash of styles and genres, but they're mostly all ridiculously good looking and talented.
(Ohh, my rambling, it gets so long...)