Here's a list of applications I use a lot. Most are free, but read the EULA's before you start deploying them to the enterprise.
Cropper - Excellent screenshot utility. Beats the hell out of opening mspaint and cropping screenshots. After running Windows 7 for a while I've found the built-in snipping tool does basically the same thing, but cropper has elegance and additional features that will keep it around for a long time. Cropper is found here.
Fiddler - A must for troubleshooting back-and-forth between client machines and web sites. I used this to troubleshoot problems with exposing SharePoint sites over the extranet. Hint: it'll show you what style sheets remote clients are being directed to in order to paint the site as you intended. Fiddler is here.
Inctrl - Bit of an older application. Ever need to write a scripted installation of a custom application? Ever wanted to see what changes an installation is making to your machine. Look for Inctrl.
KeePass - a neat utility to keep track of all your passwords in a safe manner. I use KeePass every day. It stores the URL, username, password, etc. information in a masked encrypted format. You can easily export password lists (for eventual sharing). You can also easily generate complex passwords for all your super secret credentials and then access them with simple keystrokes. You can randomly generate passwords that fit certain length and characterset parameters either by random mouse movements or keystrokes. *Highly* recommended. Get KeePass here.
Paint.NET - Very cool application for editing images. Supports what I consider basic stuff like cropping, rotation along an axis, but also really handy things like red-eye reduction. You can also turn a digital photo into a water color if you like. Very trippy. Paint.NET is available here.
PAL - A colleague (thanks J.S.) showed me this. Excellent way of elegantly displaying perfmon stats. Consolidates perfmon binaries into easy-to-read graphs. PAL is available here.
PING - A knoppix competitor, of sorts. This utility is an excellent way of backing up your drives. Plug in a USB hard drive and boot up using a slight .iso of this utility. You can reset passwords and take full image-like backups of your drives. Most external USB drive storage drivers are loaded with no hassle. I *love* this utility for performing backups. Get it here.
QuickSearcher - This utility is terrific for finding strings in files. While I don't believe the built-in Windows utility will delve into .exe and .dll files QuickSearcher does. Get it here.
Windirstat - I first heard about this in Windows IT Pro magazine and I've used it for years. If you've ever had disk space issues or wondered what was eating disk up this is the utility for you. This gives you a graphical layout of how disk space is utilized. There's also a heads-up display with the breakdown by file type. It comes highly recommended and is available here.