The first comes from ABX of The Hood Internet, a Chicago mash-up duo. Keeps true to the original "Two Weeks" with the same tempo and completely intact vocals.

Download: ABX: "Two Weeks Of Hip Hop" (Dead Prez vs. Grizzly Bear)

The second version by Tom Ato is sped up  so it sounds weird at first, but ultimately it works: Jay-Z sings at the regular tempo of "99 Problems", the Grizzly Bear vocals aren't ditched (completely), and we get Lil' Jon's "Let's go" which makes basically everything better.

Download: Grizzly Bear: "Two Weeks" (Tomato remix)

(UPDATE 4/26: download them both)

For noobs who haven't heard the original: