If you haven't seen it yet, Scott has updated his list of tools that every developer should look at. This is by far the most comprehensive list of useful utilities I've seen thus far.
I looked through my utilities I install, and I only found one that something from his list doesn't cover - Active Ports. This shows which ports are in use, and by what process. I've used this a few times when I was wondering why a certain port wasn't available.
Of course, I found one thing that wasn't on his list, but he has many, many that aren't on my list, so you should check it out. I already downloaded and installed TaskSwitchXP, and although it takes some getting used to, it's very cool. I'll be adding this to the list of things to install on my base as well as my VPC images.
Thanks, Scott! You're doing us all a huge favor!