The following are the tools which are very frequently used in SharePoint Projects.
SharePoint Designer is a WYSIWYG HTML editor and web design application from Microsoft exclusively for SharePoint sites.
Download link: http://www.microsoft.com/DOWNLOADS/details.aspx?FamilyID=baa3ad86-bfc1-4bd4-9812-d9e710d44f42&displaylang=en
U2U CAML Builder
A tool for creating and executing CAML queries
Download link: http://www.u2u.be/res/Tools/CamlQueryBuilder.aspx
SP Dispose Check
A tool for writing safe code using SharePoint Object Model to prevent memory leaks
Download link: http://code.msdn.microsoft.com/SPDisposeCheck
A tool for creating SharePoint Solution Package (WSP) WSS 3.0 & MOSS 2007
Download link: http://www.codeplex.com/wspbuilder
A tool for creating easy deployable solution
Download link: http://www.codeplex.com/stsdev
SharePoint Manager 2007
It a SharePoint object model explorer tool, enables you to browse every site on the local farm and view every property.
Download link: http://www.codeplex.com/spm
WSS/MOSS Log file reader
A tool to View, search and filter SharePoint ULS log files directly from within Central Administration.
Download link: http://www.codeplex.com/wssmosslogfilereader
SharePoint Logging Spy
A tool to allow real time diagnostics of multiple servers in a SharePoint
Download link: http://www.codeplex.com/sharepointloggingspy
SharePoint Test Data Population Tool
A tool for capacity planning and performance testing that populates data for testing SharePoint deployments
Download link: http://www.codeplex.com/sptdatapop
It is an advanced Active Directory (AD) viewer and editor which allows manipulation of AD objects
Download link: http://technet.microsoft.com/en-us/sysinternals/bb963907.aspx
IE Developer Toolbar
A tool that aims to aid in design and debugging of web pages
Download link: http://www.microsoft.com/downloads/details.aspx?FamilyId=E59C3964-672D-4511-BB3E-2D5E1DB91038&displaylang=en
Note: “Internet Explorer 8” includes the features of IE Developer Toolbar built in, instead of a separate product; known as Developer Tools rather than Developer Toolbar.
A tool for disassemble Assemblies
Download link: http://www.red-gate.com/products/reflector
A tool that helps developers writing XML documentation comments
Download link: http://www.roland-weigelt.de/ghostdoc
A tool to extract hard coded strings from the code to resource files
Download link: http://www.codeplex.com/ResourceRefactoring
It is a Web Debugging Proxy which logs all HTTP(S) traffic between your computer and the Internet.
Download link: http://www.fiddlertool.com/