I have to separate them into different catagories:
For youtube:
# 5: Justin Beiber vs Slipknot:
http://www.youtube.com/watch?v=kspPE9E1yGM
# 4: Russian Unicorn:
http://www.youtube.com/watch?v=YjaZNYSt7o03
# 3: Epic Rap Battles of History - Albert Einstein vs Stephen Hawking
http://www.youtube.com/watch?v=zn7-fVtT16k
# 2: Slaughter Your World:
http://www.youtube.com/watch?v=fcbazH6aE2g
# 1: remix to ignition (ukulele / mandolin cover)
http://www.youtube.com/watch?v=hwwAWoeAdWs
For Funny:
# 5:Arragant Worms - Johnny came home headless
# 4: Jonathan Coulton - Baby got back
# 3: The Gourds - Gin and Juice
# 2: Jonathan Coulton - First of May
# 1: Weird Al - Trigger Happy
For Serious:
# 5: Motörhead - 1916
# 4: Motörhead, Ozzy Osbourne and Slash - I ain't no nice guy
# 3: Everlast - What it's like
# 2: Nine Inch Nails - Hurt
# 1: Alice in Chains - Rooster
For Metal:
# 5: Guitar Heroes - Hellbilly
# 4: Metalica - Battery
# 3: Megadeth - Sweating Bullets
# 2: Snot - Deadfall
# 1: Judas Priest - Leather Rebel
For Alternative Rock/Grunge:
# 5: Stone Temple Pilots - Big Easy
# 4: Nirvana - Polly
# 3: Red Hot Chili Peppers - Soul to Squeeze
# 2: Sublime - What I got
# 1: Butthole Suffers - Pepper
For Oldies and Classic Rock:
# 5: Paul Simon - Late in the evening
# 4: Jim Croce - Roller Dirby Queen
# 3: The Kinks - Lola
# 2: Creedence Clearwater Revival - Looking out my back door
# 1: Pink Floyd - Comfortably Numb