These are a few apps that I have found useful for designing and developing websites. Check them out and let everybody else know how you feel about them in the comments.
I will be adding to the arsenal of tools, so check back soon.

Snippely

Snippely is a Text and Code Organizer. If you have useful text or code that you store in separate files or various bookmarks on the web, why not grab this useful app and get your code organized.

ColorPix

This is a very useful app that grabs the color information that is directly underneath your mouse.

Firebug

A Firefox add on that saves time, money, and frustration. You can find html and css information with the click of a button. This is a must have for any designer and/or developer
URL: Firebug

Dropbox

Dropbox is a sync, store, and share app that is in the clouds. Easily sync content between you and your client without the worry of uploading and downloading. Simplicity at its best
URL: Dropbox

Cropper

(PC) Cropper is a screen capture utility written in C#. It makes it fast and easy to grab parts of your screen. Have it save as a file type to a folder or capture to your clipboard. Small resource footprint.
URL: Cropper

Notepad++

Notepad++ is a free source code editor. Based on a powerful editing component Scintilla, Notepad++ is written in C++ and uses pure Win32 API and STL which ensures a higher execution speed and smaller program size. Get rid of bulky source editors and step up from basic text editors.