Photoshop CS3 (soon CS4) is the main tool that a professional should use. I know a few pros that use LightRoom v.2.0, but in terms of capabilities, CS3 is so far above the competition in terms of capabilities that it basically has no true competition.
If you are a pro, there is no reason to use anything else other than CS3.
Besides Photoshop, Adobe & Apple products, what are some of the must haves for photographers going professional and opening a studio?
Lightroom and CS3 have completely different purposes, and they offer the most when used together.