chiddy bang, I'm not surprised about that though, they're a relatively new rap duo out of Philly. I recommend 'Opposite of adults', 'Truth', or 'slow down' if anyone is looking to sample them.
Sam Adams is a new rapper out of Boston that is good, I believe he's most well known for his remix of Asher Roth's 'I Love College' though. It's called 'I hate College'
Out of curiosity do many people know about Four Year Strong? They're a great band but not many of my friends have ever heard of them.
Others artists I feel may not be very well known at least within my group of associates include: Wiz Khalifa, Cash Cash, and Phoenix.
EDIT: Chisel is a great indie band that is no longer together, but their lead singer still does solo work I believe