For music I used Deluxe Music 2 for many years. My goal was to work in a music notation environment and control midi synth devices and it did an amazing job of that. A graphics card enabling a larger display breathed new life into it as well.
I know through fame that protracker is an amazing tracker, which is another way to make music and if that is more the style of music you want to make you should check that program out for sure.
On the 3D art side, there are many programs to choose from, the most famous of course being lightwave. I spent several years dedicated to leaning Real3d and I thought it was a great program. I saw some amazing stuff done in Aladdin4D which might be good program to get into because it has a new owner now and we should be seeing a new version in the future I would guess.
On the 2D art side, check out Personal Paint as it still being developed, and check out ImageFX for image processing and manipulation.
Those are very brief starting points. The Amiga's library of software in these and other areas in vast to say the least.
