Adobe CS6 Master Collection 64bit (Photoshop)
SAI (sketching)

I personally use both Photoshop CS5-6 and Sai for painting and sketching. There is no limitations on either. However. they are both incredibly different with blending and brush styles. So really it is up to you and how you enjoy painting.

I would give both of them a try and see what you like.

I should add that they both have positives and negatives as well :>

Give Corel Painter 12 a try. The brush emulation is pretty neat, so is the option of having the "paint" dry. Should I ever get a new computer it would be the program of my choice.