The Living Legends Crew (Members: Murs, Asop, Scarub, Eligh, The Grouch, Bizarro, PSC, Sunspot Jonz) All these guys have a bunch of solo albums as well.
J Dilla (Albums: Donuts, Jay Love Japan, Ruff Draft)
Madlib (Albums: Madvillainy, Jaylib, Smoked out in the Bombshelter, Invazion, many many more)
Peanut Butter Wolf (Albums: My Vinyl Weighs a Ton, Bass your Trunk, many more)
Freestyle Fellowship (Members: Aceyalone, Mikah 9, Peace) All have albums.
Brother Ali (Albums: Shadows of the Sun, The Undisputed Truth)
Busdriver (Albums: Temporary Forever, Fear of a Black Tangent)
Galapagos 4 Crew (Members: Qwel, Robust, Qwazaar, Meaty Ogre, Offwhyte, Maker) All with albums.
2Mex (Albums: 2Mex, B-Boys in Occupied Mexico, Sweat Lodge Infinite, Smartyr with Life Rexall)
Rifleman AKA Ellay Khule (Albums: Califormula, In My Own World)
Shapeshifters Crew (Members: 2Mex, Life Rexall, Circus, Awol One, Existerio, Lewdachris, Akuma, Die) All with albums.
Visionaries Crew (Members: 2Mex, LMNO, Key Kool, Zen, Dannu, DJ Rhemmatic) All with albums.
These are all underground and hard to find, your best bet would be Newsgroups to get them. This is only a small portion of what I listen to, and all I could think of right now. Feel free to ask about any of these people and I will answer the best that I can.