My previous post outlined my exploration in text editors. But, there are several other tools that revolutionized my ability to do my job.
Skitch - shareable screenshots with the ability to draw, annotate, etc. If you are seeing an error, need to make design changes, etc. Make a screenshot in Skitch, upload it to their servers, and share the URL with those you are communicating with.
Shapes - OmniGraffle is awesome, but pricey. Shapes is a straightforward and cheap diagramming tool. This is a real quick and dirty way to share workflows and transitions. Much love for a $4.99 tool.
VMWare Fusion - Can also substitute Parallels. I am generally risk adverse, and my development environment needs to be stable to avoid introducing problems to other projects. As such, VMWare Fusion allows me to play around in a safer sandbox. I quickly spin up a Linux instance and play around. If I don't like the result, I blow away the instance.
Screenium - YouTube has taken off and people are accustomed to watching videos for demos, tutorials, and such. Screen capturing and/or personal recordings allow a dedicated way to walk someone through a complex system. Furthermore, the video can be referenced as needed by the intended audience or those down the road that may benefit from it. It's great for training materials and knowledge transfer when staff leave.
Adium - The end-all centralized chat service. Support for Google Chat, Facebook messaging, Jabber servers, IRC, AIM, Yahoo, you name it.
Dropbox - Distributed online file share services are all the rage. They provide stronger guarantees for backups, they have wide adoption for sharing files between peers, and a polished integration across many devices. Load up the Dropbox software on your iPhone, Mac, etc and have file access native to your machine. Pretty slick!
What tools do you use? I'd love to expand my horizons.