Immortal Technique is the only relatively young emcee consistently putting out new material that truly impresses me. Admittedly, I don't follow the new music scene all that closely anymore.
Sadly, I get the feeling Tech is largely only appreciated by older rap heads like myself, and is somewhat of an "underground" rapper who probably is largely unknown to high school and college age rap fans.
Representing Harlem, USA! 
A lot of people are down with Immortal, as well as Jay-Dee (RIP), and MF Doom.
It is the college age and HS that best appreciate the underground rappers. Where do you think Kanye got his biggest push from? It was the college age, and Kanye was considered a groundbreaking producer. Remember him walking around with a backpack, like he was still underground after he blew up.
Then you have guys like Clipse who are that fringe of underground and mainstream, they have sleeper albums, and so does RZA, but he's more into producing.
I mainly listen to R&B, and I have to search for the good shit, because like hip-hop, r&b is mostly garbage. It's the "neo-soul" artists that I like the most.