• Adobe Flex Builder
• Omni Group OmniGraffle
• TechSmith Camtasia for Mac
• VMware Fusion (and Windows XP running in a VM)

That's all. (As an Adobe partner, our company also has licenses for developing and testing against the Adobe Creative Suite but that's not what I use to get my work done.)

It's great that developing software (at least the web-based kind we're doing) requires almost no investments these days, aside from hardware and an Internet connection! I remember very well how frustrated I was (as a pupil and student) for not being able to program because serious money was being charged for IDEs and compilers…