What career(s) would you like to be added to TS4?

Musician along the lines of the actor career, absolutely.

I also want what I'm missing from Sims2, the ability to run a hair salon or a bar (or other entertainment venue).

I'd like playable factory and construction careers, because I think a lot could be done with them animation-wise and I would like more blue collar options. They could totally make a construction site like the acting set that changes every time or as you advance so that you can move up from plumbing through running big equipment...