This list will grow as I find new tools. So if you know of some not on this list do post them in the comments.
SQL Server Management Studio Add-in's
SSMS Tools Pack - an add-in with lots of IDE options (Query Execution history, regions, debug sections, CRUD stored procedures creation, new query templates, running custom scripts from Object explorer's context menu) for SQL Server Management Studio and SQL Server Management Studio Express
Data Scripter - generates insert statements for a table
Create Database Snapshot - simple GUI for creating a database snapshot
Sort SQL Project Files - sorts SQL project files
The Black Art of Writing a SQL Server Management Studio 2005 Add-In - a how-to article and a Search DB Objects add-in with code
How to create SSMS Add-in - an article that describes how to create add-ins without any source code
Free SQL Server books
"Boost your DBA expertise" and "DBA Best Practices" - two free books by RedGate
SQL Injection tools
Top 15 free SQL Injection Scanners - 15 free SQL injection scanners :)
Microsoft Source Code Analyzer for SQL Injection - a static code analysis tool for finding SQL Injection vulnerabilities in ASP code
UrlScan v3.0 Beta - a Microsoft security tool that restricts the types of HTTP requests that Internet Information Services (IIS) will process
HP Scrawlr - crawls a website, simultaneously analyzing the parameters of each individual web page for SQL Injection vulnerabilities
Blind Sql Injection Brute Forcer version 2 - accepts custom SQL queries as a command line parameter and it works for both integer and string based injections.
SQL Web Data Administrator - enables you to easily manage your SQL Server data from a web browser
SQL Server Cache Manager - allows you to return information about what is stored is the SQL Server cache and how efficiently it is being used.
SQL Internals Viewer - a tool for looking into the SQL Server storage engine and seeing how data is physically allocated, organized and stored.
Microsoft SQL Server 2000/2005 Management Pack - monitors the availability and performance of SQL Server 2000 and 2005 and can issue alerts for configuration problems.
Performance Analysis of Logs (PAL) Tool - tool that reads in a performance monitor counter log (any known format) and analyzes it using complex, but known thresholds (provided).
Microsoft Baseline Security Analyzer - helps small- and medium-sized businesses determine their security state in accordance with Microsoft security recommendations and offers specific remediation guidance
RML Utilities for SQL Server (x86) and (x64) - tools to help database administrators manage the performance of Microsoft SQL Server: Overview
SQLDumper.exe - comes with SQL Server. Installed at ..\Microsoft SQL Server\90\Shared\SQLDumper.exe. Generates a dump file on demand for any Microsoft Windows application.
SQL Server 2005 Partition Management - helps in data loading and extraction from partitions
SQLdiag Utility - a general purpose diagnostics collection utility that can be run as a console application or as a service (comes with SQL Server)
SQL Nexus - analyzes SQLDIAG captures
PSSDiag Utility - a general purpose diagnostic collection utility that Microsoft Product Support Services uses to collect various logs and data files
SQL Recon - performs active and passive scans of your network in order to identify all of the SQL Server/MSDE installations in your enterprise
SQL Server 2005 Express Profiler - a free SQL Profiler for SQL Express
Log Parser 2.2 - provides query access to log files, XML files and CSV files, the Event Log, the Registry, the file system, and Active Directory
Microsoft SQL Server Management Studio Express - apparently a lot of people don't know this exists. Stripped down version of SSMS
SQL Server 2005 System Views Map - a nice map of all the DMV's and links between them
SQL Server Web Data Administrator - admin your SQL Server over the web
SQL Server Express Utility - simple interaction with SQL Server
TableDiff.exe - utility that compares 2 tables for differences in data and schema for SQL Server 2000 and 2005
DMVStats - collects, analyzes and reports on SQL Server 2005 DMV performance data
Best practices, analysis, health and performance
SQL Server FineBuild - provides one-click install and best-practice configuration of SQL Server 2005.
SQL Server 2005 Assessment Configuration Pack for Sarbanes-Oxley Act (SOX) - contains configuration items intended to help you establish and validate a desired configuration for your SQL 2005 servers in order to support your Sarbanes-Oxley compliance efforts
SQLIO GUI - user interface for SQLIO Disk Subsystem Benchmark Tool
SQLQueryStress - automatically collects metrics to help you determine whether your queries will perform under load, and what kind of resource strain they put on your server
SQLIO Disk Subsystem Benchmark Tool - used to determine the I/O capacity of a given configuration
SQL Server 2005 Best Practices Analyzer - lets you verify the implementation of common Best Practices in SQL Server 2005
SQL Server 2000 Best Practices Analyzer - lets you verify the implementation of common Best Practices in SQL Server 2000
SQL Server Health and History Tool (SQLH2) - collects information from instances of SQL Server to determine how SQL Server is being used
SQL Server Health and History Tool (SQLH2) Performance Collector - optional tool to collect performance counters that are consumed by the SQLH2
SQL Server Health and History Tool (SQLH2) Reports - reports needed to view the data collected by the SQLH2
SQL Server 2005 Performance Dashboard Reports - performance reports that integrate into SQL Server Management Studio
Microsoft SQL Server 2000/2005 Management Pack - monitors the availability and performance of SQL Server 2000 and 2005 and can issue alerts for configuration problems
Database Publishing to hosted servers
Microsoft SQL Server Database Publishing Wizard - provides a way to publish databases to T-SQL scripts or directly to supporting hosting service providers
Microsoft SQL Server Database Publishing Services - deployed by shared hosting providers to enable publishing of SQL Server databases over the Internet
Upgrade and Migration
Microsoft SQL Server 2005 Upgrade Advisor - used when upgrading from lower SQL Server version to SQL Server 2005
SQL Server Migration Assistant for Access
SQL Server Migration Assistant for Oracle
SQL Server Migration Assistant for Sybase ASE
SQL Server Analysis Services
MDX Script Performance Analyser - allows the user to identify how much each calculated member, named set and scoped assignment in an Analysis Services cube's MDX script contributes to the overall performance of a given MDX query.
Microsoft SQL Server 2005 Data Mining Add-ins for Microsoft Office 2007 - SQL Server 2005 predictive analytics in Office Excel 2007 and Office Visio 2007
SQL Server Integration Services
DTLoggedExec - allows you to run a Sql Server Integration Services (SSIS) Package producing a full and detailed logging information of execution status and package runtime data.
SQL Server 2005 BI Development Studio (BIDS)
BIDS Helper - Add-in for Visual Studio Business Intelligence Development Studio
SQL Server Analysis Services Product Samples
SQL Server 2005 Samples and Sample Databases
Non MS stuff
SQL CLR Project - a tool that allows you to deploy .NET assemblies to SQL Server. Pretty COOL if you work with SQL CLR a lot
SQL Designer - online SQL Database designer. Contains Importing and Exporting scripts to and from different formats
DbDiff and DbScripting - Compare SQL Server database structures and generate scripts
SQL Accord Community Edition - compares database schema
Quest software's Comparison Suite for SQL Server - tried it... pretty slick
Bypsoft's DBTYP.NET - compares SQL Server, MySQL and Oracle databases. Cross database comparison of schemas and data.
SQL DB Tools - SqlDbDiff, SqlDbSearch and SqlDbSize utility
ClearTrace - utility to easier read your saved trace files
SQL Sripter - data export and scripting utility for Microsoft SQL Server
ScriptDb - data export and scripting utility for Microsoft SQL Server
Idera's Free Tools - SQL Server backup and recovery tool, performance dashboard and logons and permissions transfer tool
SQL and other code Formatting
Jean-Claude Manoli's code formater - online formatting. I use this for my blog's code formatting. Has source code download and formats C#, VB, HTML/XML/ASPX , T-SQL and MSH
SQLinForm - online and desktop versions
Simple Talk's Prettifier - online format tool for T-SQL, C# and VB.
Wangz's Instant SQL Formatter- formats SQL for pretty much all know databases, they also have an add-in for SSMS and QA but it's not fully free so no link :)
SQL Version Control -
red-gate source control beta