MS and other Core .NET sites.
www.gotdotnet.com - The World-Wide-Web home for .NET
asp.net - The home of (you guessed it) ASP.NET on the web.
winforms.net - The home of Windows Forms on the web.
www.dotnetnuke.com - Community Starter Kits.
Some of my favorite .NET sites. I visit most of these weekly if not daily.
Patterns and Practices - One of the absoulte best .NET resources available anywhere.
MSDN - Search it from Google, everyone else does.
The AspAlliance - Ooodles of Info, and home to a huge MS developer community.
IISFAQ - Everything you wanted to know about IIS (almost).
KBAlertz - Sign up for delivery of a daily dose of bugs/fixes/kb articles.
CodeProject - See what's cookin' in the kitchen.
LearnVisualStudio.net - A great resource for learning .NET.
Links to some Commonly used and referenced SQL Server Sites.
SQLServerVideos.com - Free SQL Server Training from a REALLY good looking guy.
SQLServerCentral - A great SQL Server and SQL Server Community resource.
SQLTeam - Links to all sorts of great SQL Server Articles and Resources.
SQLJunkies - A newer resource on the web that's shaping up quite nicely...
SS2005 - XML and Yukon. Great domain name!
SQLServerPerformance.com - Some of the best info on perf tuning out there.
A smattering of sites that house resources for all sorts of .NET related topics, like... web design, xml stuff, regex, etc...
Sites that are geared toward interactions between developers for various forms of knowledge transfer.
www.microsoft.com - It would be pretty hard to have an MS community without MS.
DevAdvice - Forums for a variety of developer topics.
asp.net/forums/ - Forums for the war on ASP.NET
AngryCoder - Great insights on coding and life as a developer.
Useful sites that provide resources for tweaking, optimizing, and customizing your workstation.
SuggestAFix.com - A forum. Bring your quirks/problems.
Annoyances.org - Think you're going nuts? Nope, it's your OS.
BlackViper.com - Excellent performance and security tweaks.
Doug Knox - Excellent scripts and utilities for XP.
Aaron Margosis' Blog - A great resource for running with least privilege.