Only a few. All I have to do is hit 'shuffle' since most of my music is composed of bands I wish were still around.

Nujabes was a godly composer/DJ and I wish he was still alive. I miss him dearly. In addition to being a mastermind solo artist, he also composed most of the music for the anime 'Samurai Champloo'.
Horizon
Luv (Sic) 2
Luv (Sic) 3
Luv (Sic) 4
Counting Stars

Shifting away from hip-hop, I recently got into Pantera and was pissed to find out they split because of Dimebag's death.
Cowboys From Hell
Walk
Mouth for War
Drag the Waters

Rolling into the realm of thrash metal, Torture was one of my favorite bands for a very, very long time. I'm sort of growing out of that phase, but I still love giving them a listen every now and again.
Ignominious Slaughter
Blood Portraits
Terror Kingdom

Moving away from that, Jawbreaker was an awesome 90's slacker-rock band [otherwise known as punk rock, or high-school-rock] that ended up splitting due to musical differences, but they kicked some serious ass.
Sluttering (May 4th)
Do You Still Hate Me?
Chemistry