For my money, one of the best composers in the music business would have to be Yuji Ohno. This guys is mostly known for his work on just about anything that has to do with Lupin III. After the last few weeks, it's hard for me not to think of Ohno's compositions when Lupin comes to mind. (I've been listening to his various albums to get my jazz fix.)
Ohno's works are primarily jazz-inspired and even some of his earliest efforts on Lupin music in the '70s is still considered extraordinary. Not only has he covered music for the various Lupin series and movies, he's also done music for all three PS2 Lupin games.
The man is also an accomplished musical genius even when he isn't working on music for Lupin. Tokyo City Lights is a jazz masterpiece.
If you want to hear some of Ohno's work, just check out this YouTube page with various uploads.