These lists will now be maintaned in the Cool Tools discussion forum.
Please join us and tell us your favourite Cool Tools for .NET Development.
File/Directory Comparison Tools

• WinMerge
• Same as the old Windiff that used to ship with MS Visual Studio but can selectively merge each diff from one file to the other ... and lots more.
• 
  
TreeComp
• The ultimate directory comparison / synchronisation tool and it's free!
• Can compare local files/directories, ZIPS, or FTP directories using multithreading.
• Don't get put off by the few
window resizing bugs.  This tool is extremely feature complete and otherwise very stable.
• Configure TreeComp to use WinMerge to compare files (in place of the default Windiff) and you have the killer free comparison suite.
• My
main whinge is that it can tend to lock files and directories so you might find you occasionally need to close it when updating the compared files outside TreeComp.

Text Editor

• 
  
TextPad is my editor of choice for software development.
• Fully customisable syntax highlighting for most programming languages.
• Many features are customisable by file type (e.g. tabbing)
• Spell checker, sorting, macros, clip libraries..
• Auto detects and preserves PC/Unix/Mac text file formats.
• Binary file editor built in.
• Regular expression searching/replacing, recursive directory searches, double-click to view/edit a search result.
• Customisable
for each file type including: Syntax colouring, fonts, printing, tabulation.
• Customisable keyboard settings with all the common editor configs (I usually set it to "Microsoft Applications" so it behaves like Visual Studio and other MS apps).  Note: This is not the installation default.
• Good value shareware.

FTP Client

• 
  
FileZilla - My preferred FTP client.  I used to be a fan of WS-FTP until I found this superior open source replacement.
• Maintains a multi-threaded upload/download file copy queue so you can start the file copying and then add more files/directories while its running.
• Builds & caches a tree of directories it has discovered on the remote FTP site.
• I've watched this little beauty auto-relogin and resume dropped FTP sessions.  Cool!

Anti-Spam weapons

• Mail Washer
• Read your email before downloading it from the server
• Delete, Bounce, Analyse, Filter, Blacklist, Whitelist (friends),
• Good Free version.  Minimal cost to remove the ad.
• http://www.spammotel.com/
• Generates an unlimited number of unique email alias addresses that all forward email to your real email address.  Use it every time you're forced to give away your email for things like software downloads, subscriptions etc.
• You can remove/suspend an email alias if its ever abused.
• You can track who gave away your email alias to another 3rd party because every forwarded email is prefixed with a descritpion of where you gave it away (I use the signup URL page)
• Sign up for free - Read their FAQ for full details.
• Windows users can get their desktop app.
• My only whinges are that they don't use SSL security to send passwords (so chose a new password you can afford to loose) and you can't change your password!
• 
  
POPfile (open source)
• Automatic mail classification tool that "learns" how to classify your e-mail.
• Supported on Windows and Linux for most E-mail clients (e.g. Outlook Express, Eudora etc. ).
• I tend to depend on this less now that I use Mail Washer.