MIXTAPES.

Mixtapes are cd's that contains underground, un-officailly released songs from some of your favorites artist. They release street songs on this cd's to keep their buzz going.
The cd's are collaborative efforts from artist and dj, and sometimes, it might be a dj, compiling songs from a lot of rappers, street songs, or songs yet to be released to the mainstream.
This is the medium that lil wayne used to come up and gain acceptance and he is still using it.
5ocent and his G-Unit family also used this medium to reach out to their fans constantly.
If you are a rapper, and you want to drop a mixtapes every two months, then it's up to you to keep up.
While a cd cost about 13 dollars, mixtapes cost between 5-7dollars.
Artist like jadakiss, styles p, and sheek louch also operate in this circle with their D-Block imprint(a group and also a record label comprising of jadakiss, style p, sheek louch, bully and various dj's like super mario, liveson,).
Currently, lil wayne is on number 1 and number 2 of the mixtapes chart, with two of his mixtapes, " dj drama and lil wayne, dedication 3" and "dj keyz and lil wayne, waynes world vol 3"
An artist like papoose has to thank this medium, because asides appearing on other people's songs, he has no solo album, but currently has 17 mixtapes released in his name so far.
Lil Wayne is constantly the king of mixtapes. The kid has a mixtape out almost every time of the year, and is constantly on top of he mixtapes charts. You would think he would run out of flows.
The game is another rapper that uses these medium frequently to showcase his talent, let the world hear his black wall street rappers and must importantly, address beefs.
Between 2005 and 2006, the game dropped more than 4 mixtapes to address the 50cent and g-unit beef alone.