Below you find my most valuable SQL Server and database related links. To make it a bit easier to find what you are looking for, I have categorized the links. Click on a category to display the links.
Glenn Berry's SQL Server Performance, including DMV diagnostics queries
Erland Sommarskog's in-depth articles about dynamic SQL, arrays in SQL, error handling etc.
Brent Ozar, sp_BLITZ
Ola Hallengren's solution for SQL Server backup, integrity check and index optimization
SDU Tools, lots of useful functions from Greg Low
Contribute changes to Books Online
Free deadlock collector and parser, by Andreas Wolter
Essential SQL, good basic into of SQL (the language), normalization, etc.
Lots of connection string examples
PASS - The Professional Association for SQL Server
Query store custom SSMS performance dashboard
SQL Server KIT, including trace flag list, Konstantin Taranov
Stairways on SQL Server Central
Links to SQL Server Feature Packs, from AKAWN
Most recent update of SQL Server
Version history, sqlserverbuilds.blogspot.com
SQL Release Services Blog, find recent releases
Data modeling tool, SqlDBM
ApexSQL Log, retrieve data from transaction log
Tiger Team's toolbox
SysTool's SQL Log Analyzer
Poor TSQL Formatter
Stuff you pay for.
Home page (check out the blogs from the members)Wait Types LibraryLatch Classes Library
Component listing on CodeplexSQLIS.com - By Darren Green and Allan Mitchell
SQL Server e-book gallerySQL Server virtual labsSQL Server LicensingMicrosoft SQL Server HomeConnect: Microsoft SQL Server FeedbackDatabase Engine Permission Basics
Library of Free Data ModelsDatabase DebunkingsThe Data Administration Newsletter (TDAN.com) FoyerIntelligent Versus Surrogate Keys
NIST Dictionary of Algorithms, Data Structures, and ProblemsSysinternals utilitiesDependency walker