I can think of a lot of web development tools I swear AT – 
but what little known web development software programs and tools do you find extremely helpful and couldn’t possibly live without?
Firefox for development and the following addon which instantly validates your HTML code.
http://users.skynet.be/mgueury/mozilla/new_upgrade.html
And a good editor with syntax highlighting such as UltraEdit or HippoEdit.
Axialis IconWorkshop - Great product, Use it mainly for producing Favicons / App Icons.
ColorSchemer Studio - Single best color application in existence, great for web design.
MainType - Font organizer, use it for deciding what typefaces to use within designs.
MyLife Organized - Organizes my workflow, best to-do list application going.
SmartFTP Client - Again, another tool I live by, use it for uploading stuff to my site.
Snagit - Screenshot application, fantastic tool for getting images ready for articles.
SWiSH Max - Alternative to Flash, more simple, quick and easy to use application.
Oh I love Snagit! I expect a scrolling screenshot every time I hit the print screen key 
Love ColorSchemer too!
Anything else?
Have you tried Graabr.com - it is free to use indefinitely, only 1.14 Meg download and ever so easy to use.
.
I use a range of open source and freeware tools too:
Audacity, Dia, GIMP, iFreeBudget, InkScape, KeePass, Notepad++, Paint.NET, Scribus, Skype, TweetDeck, WinMerge and Xenu Link Sleuth.