Nerdcore Hip-hop is a subgenre of Hip Hop defined, not my stylistic similarities, but instead by subject matter. The subject? Nerd Stuff. It can range from computer science to intellectual and a lot of stuff in between.
the genre has its roots in nerd rock (think Weezer's song "In the Garage") and *sign* filk. Weird Al's "It's All About the Pentiums" is a good example of an early example of Nerdcore.
Like many niche musical movements, the music is self produced and self distributed. A network of websites has grown up over the the last few years to help generate traffic to artists websites.
If you want to know more, google is awesome. Nerdcore hip hop is made by nerds, so the web is a good place to start. I've put together a mixtap of some of my favorite stuff, email me and I can send a link where you can download it.
MC Hawking (the gangster rap version of Stephen Hawking)
MC Lars (music based on post punk and emo samples)
Optimus Rhyme (transforms anymore?)
All these guys have myspace pages and free .mp3s on their websites but NerdCoreHiphop.org hosts a bunch of mix-tapes.