For slides, try Kodak E100G, Velvia if you like that look, Provia 100F, Astia 100F (lower contrast, nice colors), and Provia 400X (best 400 speed slide).
For color negative (which I personally cannot really stand), everyone raves about the new Ektar 100. The Portra and Fuji Pro NS/VS films are the other professional standards.
For black and white there is a lot more choice. My personal favorite is Fuji Acros, which is an astoundingly good film -- the finest grain of any 100 speed black and white, a very good tonal range, very sharp, forgiving processing in many developers, and the least reciprocity failure of normal black and white films. In 120, like the rest of Fuji films it is easier to load and unload since it has a locking paper tab (so the film stays on the spool automatically), and hand rip-able debris free tape holding the film on the backing. It is a technological tour de force. A lot of these things you will not appreciate if you don't process for yourself, but it is really a film that people who developed a lot can learn to love!
Other than that, if you like traditional emulsions, try Pan F+, FP4+, Fuji Neopan 400 or Tri-X. There are many other nice films to choose from, but those are some good places to start. It is very hard to go wrong with any of the films from Fuji, Kodak and Ilford.