Active Ports et al. - ports monitoring tools
http://www.protect-me.com/download.html

a-squared (a2) - Malware detection tool
http://www.emsisoft.com/en/

AvantBrowser - Tabbed interface for Internet Explorer, see also: Maxthon (aka MyIE2)
http://www.avantbrowser.com/

DeepBurner - simple & easy CD-burning
http://www.deepburner.com/
 
Desktop Sidebar - great Longhorn-like sidebar!
http://www.desktopsidebar.com/

HotBot Desktop - document searcher
http://www.hotbot.com/tools/desktop/
 
Lavasoft Ad-aware - spyware killer
http://www.lavasoftusa.com/software/adaware/

LookOut - great searcher add-in for Office Outlook
http://www.lookoutsoft.com
 
Maxthon - tabbed interface for Internet Explorer like AvantBrowser (great app too)
http://www.maxthon.com/
 
SharpDevelop - opensource IDE for C# & VB.NET
http://www.icsharpcode.net/OpenSource/SD/Default.aspx

Skype - Internet telephony, great audio, firewall-friendly
http://www.skype.com/
 
SmartBarXP - Longhorn-like desktop sidebar
http://www.smartbarxp.com - but also try Desktop Sidebar.
 
Snippet Compiler - mini-VS.NET
http://www.sliver.com/dotnet/SnippetCompiler/
 
Spybot Search & Destroy - spyware killer
http://www.safer-networking.org

SymmTime - configurable world clocks, a must-have for virtual meetings, chats, and so on
http://www.ntp-systems.com/symmtime.asp